Master: volume assignment concurrency (#7159)

* volume assginment concurrency

* accurate tests

* ensure uniqness

* reserve atomically

* address comments

* atomic

* ReserveOneVolumeForReservation

* duplicated

* Update weed/topology/node.go

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Update weed/topology/node.go

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* atomic counter

* dedup

* select the appropriate functions based on the useReservations flag

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

10 files changed, 1086 insertions, 32 deletions

diff --git a/weed/topology/capacity_reservation_test.go b/weed/topology/capacity_reservation_test.go
new file mode 100644
index 000000000..38cb14c50
--- /dev/null
+++ b/weed/topology/capacity_reservation_test.go
@@ -0,0 +1,215 @@
+package topology
+
+import (
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/seaweedfs/seaweedfs/weed/storage/types"
+)
+
+func TestCapacityReservations_BasicOperations(t *testing.T) {
+	cr := newCapacityReservations()
+	diskType := types.HardDriveType
+
+	// Test initial state
+	if count := cr.getReservedCount(diskType); count != 0 {
+		t.Errorf("Expected 0 reserved count initially, got %d", count)
+	}
+
+	// Test add reservation
+	reservationId := cr.addReservation(diskType, 5)
+	if reservationId == "" {
+		t.Error("Expected non-empty reservation ID")
+	}
+
+	if count := cr.getReservedCount(diskType); count != 5 {
+		t.Errorf("Expected 5 reserved count, got %d", count)
+	}
+
+	// Test multiple reservations
+	cr.addReservation(diskType, 3)
+	if count := cr.getReservedCount(diskType); count != 8 {
+		t.Errorf("Expected 8 reserved count after second reservation, got %d", count)
+	}
+
+	// Test remove reservation
+	success := cr.removeReservation(reservationId)
+	if !success {
+		t.Error("Expected successful removal of existing reservation")
+	}
+
+	if count := cr.getReservedCount(diskType); count != 3 {
+		t.Errorf("Expected 3 reserved count after removal, got %d", count)
+	}
+
+	// Test remove non-existent reservation
+	success = cr.removeReservation("non-existent-id")
+	if success {
+		t.Error("Expected failure when removing non-existent reservation")
+	}
+}
+
+func TestCapacityReservations_ExpiredCleaning(t *testing.T) {
+	cr := newCapacityReservations()
+	diskType := types.HardDriveType
+
+	// Add reservations and manipulate their creation time
+	reservationId1 := cr.addReservation(diskType, 3)
+	reservationId2 := cr.addReservation(diskType, 2)
+
+	// Make one reservation "old"
+	cr.Lock()
+	if reservation, exists := cr.reservations[reservationId1]; exists {
+		reservation.createdAt = time.Now().Add(-10 * time.Minute) // 10 minutes ago
+	}
+	cr.Unlock()
+
+	// Clean expired reservations (5 minute expiration)
+	cr.cleanExpiredReservations(5 * time.Minute)
+
+	// Only the non-expired reservation should remain
+	if count := cr.getReservedCount(diskType); count != 2 {
+		t.Errorf("Expected 2 reserved count after cleaning, got %d", count)
+	}
+
+	// Verify the right reservation was kept
+	if !cr.removeReservation(reservationId2) {
+		t.Error("Expected recent reservation to still exist")
+	}
+
+	if cr.removeReservation(reservationId1) {
+		t.Error("Expected old reservation to be cleaned up")
+	}
+}
+
+func TestCapacityReservations_DifferentDiskTypes(t *testing.T) {
+	cr := newCapacityReservations()
+
+	// Add reservations for different disk types
+	cr.addReservation(types.HardDriveType, 5)
+	cr.addReservation(types.SsdType, 3)
+
+	// Check counts are separate
+	if count := cr.getReservedCount(types.HardDriveType); count != 5 {
+		t.Errorf("Expected 5 HDD reserved count, got %d", count)
+	}
+
+	if count := cr.getReservedCount(types.SsdType); count != 3 {
+		t.Errorf("Expected 3 SSD reserved count, got %d", count)
+	}
+}
+
+func TestNodeImpl_ReservationMethods(t *testing.T) {
+	// Create a test data node
+	dn := NewDataNode("test-node")
+	diskType := types.HardDriveType
+
+	// Set up some capacity
+	diskUsage := dn.diskUsages.getOrCreateDisk(diskType)
+	diskUsage.maxVolumeCount = 10
+	diskUsage.volumeCount = 5 // 5 volumes free initially
+
+	option := &VolumeGrowOption{DiskType: diskType}
+
+	// Test available space calculation
+	available := dn.AvailableSpaceFor(option)
+	if available != 5 {
+		t.Errorf("Expected 5 available slots, got %d", available)
+	}
+
+	availableForReservation := dn.AvailableSpaceForReservation(option)
+	if availableForReservation != 5 {
+		t.Errorf("Expected 5 available slots for reservation, got %d", availableForReservation)
+	}
+
+	// Test successful reservation
+	reservationId, success := dn.TryReserveCapacity(diskType, 3)
+	if !success {
+		t.Error("Expected successful reservation")
+	}
+	if reservationId == "" {
+		t.Error("Expected non-empty reservation ID")
+	}
+
+	// Available space should be reduced by reservations
+	availableForReservation = dn.AvailableSpaceForReservation(option)
+	if availableForReservation != 2 {
+		t.Errorf("Expected 2 available slots after reservation, got %d", availableForReservation)
+	}
+
+	// Base available space should remain unchanged
+	available = dn.AvailableSpaceFor(option)
+	if available != 5 {
+		t.Errorf("Expected base available to remain 5, got %d", available)
+	}
+
+	// Test reservation failure when insufficient capacity
+	_, success = dn.TryReserveCapacity(diskType, 3)
+	if success {
+		t.Error("Expected reservation failure due to insufficient capacity")
+	}
+
+	// Test release reservation
+	dn.ReleaseReservedCapacity(reservationId)
+	availableForReservation = dn.AvailableSpaceForReservation(option)
+	if availableForReservation != 5 {
+		t.Errorf("Expected 5 available slots after release, got %d", availableForReservation)
+	}
+}
+
+func TestNodeImpl_ConcurrentReservations(t *testing.T) {
+	dn := NewDataNode("test-node")
+	diskType := types.HardDriveType
+
+	// Set up capacity
+	diskUsage := dn.diskUsages.getOrCreateDisk(diskType)
+	diskUsage.maxVolumeCount = 10
+	diskUsage.volumeCount = 0 // 10 volumes free initially
+
+	// Test concurrent reservations using goroutines
+	var wg sync.WaitGroup
+	var reservationIds sync.Map
+	concurrentRequests := 10
+	wg.Add(concurrentRequests)
+
+	for i := 0; i < concurrentRequests; i++ {
+		go func(i int) {
+			defer wg.Done()
+			if reservationId, success := dn.TryReserveCapacity(diskType, 1); success {
+				reservationIds.Store(reservationId, true)
+				t.Logf("goroutine %d: Successfully reserved %s", i, reservationId)
+			} else {
+				t.Errorf("goroutine %d: Expected successful reservation", i)
+			}
+		}(i)
+	}
+
+	wg.Wait()
+
+	// Should have no more capacity
+	option := &VolumeGrowOption{DiskType: diskType}
+	if available := dn.AvailableSpaceForReservation(option); available != 0 {
+		t.Errorf("Expected 0 available slots after all reservations, got %d", available)
+		// Debug: check total reserved
+		reservedCount := dn.capacityReservations.getReservedCount(diskType)
+		t.Logf("Debug: Total reserved count: %d", reservedCount)
+	}
+
+	// Next reservation should fail
+	_, success := dn.TryReserveCapacity(diskType, 1)
+	if success {
+		t.Error("Expected reservation failure when at capacity")
+	}
+
+	// Release all reservations
+	reservationIds.Range(func(key, value interface{}) bool {
+		dn.ReleaseReservedCapacity(key.(string))
+		return true
+	})
+
+	// Should have full capacity back
+	if available := dn.AvailableSpaceForReservation(option); available != 10 {
+		t.Errorf("Expected 10 available slots after releasing all, got %d", available)
+	}
+}
diff --git a/weed/topology/data_center.go b/weed/topology/data_center.go
index 03fe20c10..e036621b4 100644
--- a/weed/topology/data_center.go
+++ b/weed/topology/data_center.go
@@ -1,9 +1,10 @@
 package topology
 
 import (
-	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
 	"slices"
 	"strings"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
 )
 
 type DataCenter struct {
@@ -16,6 +17,7 @@ func NewDataCenter(id string) *DataCenter {
 	dc.nodeType = "DataCenter"
 	dc.diskUsages = newDiskUsages()
 	dc.children = make(map[NodeId]Node)
+	dc.capacityReservations = newCapacityReservations()
 	dc.NodeImpl.value = dc
 	return dc
 }
diff --git a/weed/topology/data_node.go b/weed/topology/data_node.go
index 3103dc207..4f2dbe464 100644
--- a/weed/topology/data_node.go
+++ b/weed/topology/data_node.go
@@ -30,6 +30,7 @@ func NewDataNode(id string) *DataNode {
 	dn.nodeType = "DataNode"
 	dn.diskUsages = newDiskUsages()
 	dn.children = make(map[NodeId]Node)
+	dn.capacityReservations = newCapacityReservations()
 	dn.NodeImpl.value = dn
 	return dn
 }
diff --git a/weed/topology/node.go b/weed/topology/node.go
index aa178b561..60e7427af 100644
--- a/weed/topology/node.go
+++ b/weed/topology/node.go
@@ -2,6 +2,7 @@ package topology
 
 import (
 	"errors"
+	"fmt"
 	"math/rand/v2"
 	"strings"
 	"sync"
@@ -16,15 +17,124 @@ import (
 )
 
 type NodeId string
+
+// CapacityReservation represents a temporary reservation of capacity
+type CapacityReservation struct {
+	reservationId string
+	diskType      types.DiskType
+	count         int64
+	createdAt     time.Time
+}
+
+// CapacityReservations manages capacity reservations for a node
+type CapacityReservations struct {
+	sync.RWMutex
+	reservations   map[string]*CapacityReservation
+	reservedCounts map[types.DiskType]int64
+}
+
+func newCapacityReservations() *CapacityReservations {
+	return &CapacityReservations{
+		reservations:   make(map[string]*CapacityReservation),
+		reservedCounts: make(map[types.DiskType]int64),
+	}
+}
+
+func (cr *CapacityReservations) addReservation(diskType types.DiskType, count int64) string {
+	cr.Lock()
+	defer cr.Unlock()
+
+	return cr.doAddReservation(diskType, count)
+}
+
+func (cr *CapacityReservations) removeReservation(reservationId string) bool {
+	cr.Lock()
+	defer cr.Unlock()
+
+	if reservation, exists := cr.reservations[reservationId]; exists {
+		delete(cr.reservations, reservationId)
+		cr.decrementCount(reservation.diskType, reservation.count)
+		return true
+	}
+	return false
+}
+
+func (cr *CapacityReservations) getReservedCount(diskType types.DiskType) int64 {
+	cr.RLock()
+	defer cr.RUnlock()
+
+	return cr.reservedCounts[diskType]
+}
+
+// decrementCount is a helper to decrement reserved count and clean up zero entries
+func (cr *CapacityReservations) decrementCount(diskType types.DiskType, count int64) {
+	cr.reservedCounts[diskType] -= count
+	// Clean up zero counts to prevent map growth
+	if cr.reservedCounts[diskType] <= 0 {
+		delete(cr.reservedCounts, diskType)
+	}
+}
+
+// doAddReservation is a helper to add a reservation, assuming the lock is already held
+func (cr *CapacityReservations) doAddReservation(diskType types.DiskType, count int64) string {
+	now := time.Now()
+	reservationId := fmt.Sprintf("%s-%d-%d-%d", diskType, count, now.UnixNano(), rand.Int64())
+	cr.reservations[reservationId] = &CapacityReservation{
+		reservationId: reservationId,
+		diskType:      diskType,
+		count:         count,
+		createdAt:     now,
+	}
+	cr.reservedCounts[diskType] += count
+	return reservationId
+}
+
+// tryReserveAtomic atomically checks available space and reserves if possible
+func (cr *CapacityReservations) tryReserveAtomic(diskType types.DiskType, count int64, availableSpaceFunc func() int64) (reservationId string, success bool) {
+	cr.Lock()
+	defer cr.Unlock()
+
+	// Check available space under lock
+	currentReserved := cr.reservedCounts[diskType]
+	availableSpace := availableSpaceFunc() - currentReserved
+
+	if availableSpace >= count {
+		// Create and add reservation atomically
+		return cr.doAddReservation(diskType, count), true
+	}
+
+	return "", false
+}
+
+func (cr *CapacityReservations) cleanExpiredReservations(expirationDuration time.Duration) {
+	cr.Lock()
+	defer cr.Unlock()
+
+	now := time.Now()
+	for id, reservation := range cr.reservations {
+		if now.Sub(reservation.createdAt) > expirationDuration {
+			delete(cr.reservations, id)
+			cr.decrementCount(reservation.diskType, reservation.count)
+			glog.V(1).Infof("Cleaned up expired capacity reservation: %s", id)
+		}
+	}
+}
+
 type Node interface {
 	Id() NodeId
 	String() string
 	AvailableSpaceFor(option *VolumeGrowOption) int64
 	ReserveOneVolume(r int64, option *VolumeGrowOption) (*DataNode, error)
+	ReserveOneVolumeForReservation(r int64, option *VolumeGrowOption) (*DataNode, error)
 	UpAdjustDiskUsageDelta(diskType types.DiskType, diskUsage *DiskUsageCounts)
 	UpAdjustMaxVolumeId(vid needle.VolumeId)
 	GetDiskUsages() *DiskUsages
 
+	// Capacity reservation methods for avoiding race conditions
+	TryReserveCapacity(diskType types.DiskType, count int64) (reservationId string, success bool)
+	ReleaseReservedCapacity(reservationId string)
+	AvailableSpaceForReservation(option *VolumeGrowOption) int64
+
 	GetMaxVolumeId() needle.VolumeId
 	SetParent(Node)
 	LinkChildNode(node Node)
@@ -52,6 +162,9 @@ type NodeImpl struct {
 	//for rack, data center, topology
 	nodeType string
 	value    interface{}
+
+	// capacity reservations to prevent race conditions during volume creation
+	capacityReservations *CapacityReservations
 }
 
 func (n *NodeImpl) GetDiskUsages() *DiskUsages {
@@ -164,6 +277,42 @@ func (n *NodeImpl) AvailableSpaceFor(option *VolumeGrowOption) int64 {
 	}
 	return freeVolumeSlotCount
 }
+
+// AvailableSpaceForReservation returns available space considering existing reservations
+func (n *NodeImpl) AvailableSpaceForReservation(option *VolumeGrowOption) int64 {
+	baseAvailable := n.AvailableSpaceFor(option)
+	reservedCount := n.capacityReservations.getReservedCount(option.DiskType)
+	return baseAvailable - reservedCount
+}
+
+// TryReserveCapacity attempts to atomically reserve capacity for volume creation
+func (n *NodeImpl) TryReserveCapacity(diskType types.DiskType, count int64) (reservationId string, success bool) {
+	const reservationTimeout = 5 * time.Minute // TODO: make this configurable
+
+	// Clean up any expired reservations first
+	n.capacityReservations.cleanExpiredReservations(reservationTimeout)
+
+	// Atomically check and reserve space
+	option := &VolumeGrowOption{DiskType: diskType}
+	reservationId, success = n.capacityReservations.tryReserveAtomic(diskType, count, func() int64 {
+		return n.AvailableSpaceFor(option)
+	})
+
+	if success {
+		glog.V(1).Infof("Reserved %d capacity for diskType %s on node %s: %s", count, diskType, n.Id(), reservationId)
+	}
+
+	return reservationId, success
+}
+
+// ReleaseReservedCapacity releases a previously reserved capacity
+func (n *NodeImpl) ReleaseReservedCapacity(reservationId string) {
+	if n.capacityReservations.removeReservation(reservationId) {
+		glog.V(1).Infof("Released capacity reservation on node %s: %s", n.Id(), reservationId)
+	} else {
+		glog.V(1).Infof("Attempted to release non-existent reservation on node %s: %s", n.Id(), reservationId)
+	}
+}
 func (n *NodeImpl) SetParent(node Node) {
 	n.parent = node
 }
@@ -186,10 +335,24 @@ func (n *NodeImpl) GetValue() interface{} {
 }
 
 func (n *NodeImpl) ReserveOneVolume(r int64, option *VolumeGrowOption) (assignedNode *DataNode, err error) {
+	return n.reserveOneVolumeInternal(r, option, false)
+}
+
+// ReserveOneVolumeForReservation selects a node using reservation-aware capacity checks
+func (n *NodeImpl) ReserveOneVolumeForReservation(r int64, option *VolumeGrowOption) (assignedNode *DataNode, err error) {
+	return n.reserveOneVolumeInternal(r, option, true)
+}
+
+func (n *NodeImpl) reserveOneVolumeInternal(r int64, option *VolumeGrowOption, useReservations bool) (assignedNode *DataNode, err error) {
 	n.RLock()
 	defer n.RUnlock()
 	for _, node := range n.children {
-		freeSpace := node.AvailableSpaceFor(option)
+		var freeSpace int64
+		if useReservations {
+			freeSpace = node.AvailableSpaceForReservation(option)
+		} else {
+			freeSpace = node.AvailableSpaceFor(option)
+		}
 		// fmt.Println("r =", r, ", node =", node, ", freeSpace =", freeSpace)
 		if freeSpace <= 0 {
 			continue
@@ -197,7 +360,13 @@ func (n *NodeImpl) ReserveOneVolume(r int64, option *VolumeGrowOption) (assigned
 		if r >= freeSpace {
 			r -= freeSpace
 		} else {
-			if node.IsDataNode() && node.AvailableSpaceFor(option) > 0 {
+			var hasSpace bool
+			if useReservations {
+				hasSpace = node.IsDataNode() && node.AvailableSpaceForReservation(option) > 0
+			} else {
+				hasSpace = node.IsDataNode() && node.AvailableSpaceFor(option) > 0
+			}
+			if hasSpace {
 				// fmt.Println("vid =", vid, " assigned to node =", node, ", freeSpace =", node.FreeSpace())
 				dn := node.(*DataNode)
 				if dn.IsTerminating {
@@ -205,7 +374,11 @@ func (n *NodeImpl) ReserveOneVolume(r int64, option *VolumeGrowOption) (assigned
 				}
 				return dn, nil
 			}
-			assignedNode, err = node.ReserveOneVolume(r, option)
+			if useReservations {
+				assignedNode, err = node.ReserveOneVolumeForReservation(r, option)
+			} else {
+				assignedNode, err = node.ReserveOneVolume(r, option)
+			}
 			if err == nil {
 				return
 			}
diff --git a/weed/topology/race_condition_stress_test.go b/weed/topology/race_condition_stress_test.go
new file mode 100644
index 000000000..a60f0a32a
--- /dev/null
+++ b/weed/topology/race_condition_stress_test.go
@@ -0,0 +1,306 @@
+package topology
+
+import (
+	"fmt"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/seaweedfs/seaweedfs/weed/sequence"
+	"github.com/seaweedfs/seaweedfs/weed/storage/super_block"
+	"github.com/seaweedfs/seaweedfs/weed/storage/types"
+)
+
+// TestRaceConditionStress simulates the original issue scenario:
+// High concurrent writes causing capacity misjudgment
+func TestRaceConditionStress(t *testing.T) {
+	// Create a cluster similar to the issue description:
+	// 3 volume servers, 200GB each, 5GB volume limit = 40 volumes max per server
+	const (
+		numServers          = 3
+		volumeLimitMB       = 5000                                      // 5GB in MB
+		storagePerServerGB  = 200                                       // 200GB per server
+		maxVolumesPerServer = storagePerServerGB * 1024 / volumeLimitMB // 200*1024/5000 = 40
+		concurrentRequests  = 50                                        // High concurrency like the issue
+	)
+
+	// Create test topology
+	topo := NewTopology("weedfs", sequence.NewMemorySequencer(), uint64(volumeLimitMB)*1024*1024, 5, false)
+
+	dc := NewDataCenter("dc1")
+	topo.LinkChildNode(dc)
+	rack := NewRack("rack1")
+	dc.LinkChildNode(rack)
+
+	// Create 3 volume servers with realistic capacity
+	servers := make([]*DataNode, numServers)
+	for i := 0; i < numServers; i++ {
+		dn := NewDataNode(fmt.Sprintf("server%d", i+1))
+		rack.LinkChildNode(dn)
+
+		// Set up disk with capacity for 40 volumes
+		disk := NewDisk(types.HardDriveType.String())
+		disk.diskUsages.getOrCreateDisk(types.HardDriveType).maxVolumeCount = maxVolumesPerServer
+		dn.LinkChildNode(disk)
+
+		servers[i] = dn
+	}
+
+	vg := NewDefaultVolumeGrowth()
+	rp, _ := super_block.NewReplicaPlacementFromString("000") // Single replica like the issue
+
+	option := &VolumeGrowOption{
+		Collection:       "test-bucket-large", // Same collection name as issue
+		ReplicaPlacement: rp,
+		DiskType:         types.HardDriveType,
+	}
+
+	// Track results
+	var successfulAllocations int64
+	var failedAllocations int64
+	var totalVolumesCreated int64
+
+	var wg sync.WaitGroup
+
+	// Launch concurrent volume creation requests
+	startTime := time.Now()
+	for i := 0; i < concurrentRequests; i++ {
+		wg.Add(1)
+		go func(requestId int) {
+			defer wg.Done()
+
+			// This is the critical test: multiple threads trying to allocate simultaneously
+			servers, reservation, err := vg.findEmptySlotsForOneVolume(topo, option, true)
+
+			if err != nil {
+				atomic.AddInt64(&failedAllocations, 1)
+				t.Logf("Request %d failed: %v", requestId, err)
+				return
+			}
+
+			// Simulate volume creation delay (like in real scenario)
+			time.Sleep(time.Millisecond * 50)
+
+			// Simulate successful volume creation
+			for _, server := range servers {
+				disk := server.children[NodeId(types.HardDriveType.String())].(*Disk)
+				deltaDiskUsage := &DiskUsageCounts{
+					volumeCount: 1,
+				}
+				disk.UpAdjustDiskUsageDelta(types.HardDriveType, deltaDiskUsage)
+				atomic.AddInt64(&totalVolumesCreated, 1)
+			}
+
+			// Release reservations (simulates successful registration)
+			reservation.releaseAllReservations()
+			atomic.AddInt64(&successfulAllocations, 1)
+
+		}(i)
+	}
+
+	wg.Wait()
+	duration := time.Since(startTime)
+
+	// Verify results
+	t.Logf("Test completed in %v", duration)
+	t.Logf("Successful allocations: %d", successfulAllocations)
+	t.Logf("Failed allocations: %d", failedAllocations)
+	t.Logf("Total volumes created: %d", totalVolumesCreated)
+
+	// Check capacity limits are respected
+	totalCapacityUsed := int64(0)
+	for i, server := range servers {
+		disk := server.children[NodeId(types.HardDriveType.String())].(*Disk)
+		volumeCount := disk.diskUsages.getOrCreateDisk(types.HardDriveType).volumeCount
+		totalCapacityUsed += volumeCount
+
+		t.Logf("Server %d: %d volumes (max: %d)", i+1, volumeCount, maxVolumesPerServer)
+
+		// Critical test: No server should exceed its capacity
+		if volumeCount > maxVolumesPerServer {
+			t.Errorf("RACE CONDITION DETECTED: Server %d exceeded capacity: %d > %d",
+				i+1, volumeCount, maxVolumesPerServer)
+		}
+	}
+
+	// Verify totals make sense
+	if totalVolumesCreated != totalCapacityUsed {
+		t.Errorf("Volume count mismatch: created=%d, actual=%d", totalVolumesCreated, totalCapacityUsed)
+	}
+
+	// The total should never exceed the cluster capacity (120 volumes for 3 servers × 40 each)
+	maxClusterCapacity := int64(numServers * maxVolumesPerServer)
+	if totalCapacityUsed > maxClusterCapacity {
+		t.Errorf("RACE CONDITION DETECTED: Cluster capacity exceeded: %d > %d",
+			totalCapacityUsed, maxClusterCapacity)
+	}
+
+	// With reservations, we should have controlled allocation
+	// Total requests = successful + failed should equal concurrentRequests
+	if successfulAllocations+failedAllocations != concurrentRequests {
+		t.Errorf("Request count mismatch: success=%d + failed=%d != total=%d",
+			successfulAllocations, failedAllocations, concurrentRequests)
+	}
+
+	t.Logf("✅ Race condition test passed: Capacity limits respected with %d concurrent requests",
+		concurrentRequests)
+}
+
+// TestCapacityJudgmentAccuracy verifies that the capacity calculation is accurate
+// under various load conditions
+func TestCapacityJudgmentAccuracy(t *testing.T) {
+	// Create a single server with known capacity
+	topo := NewTopology("weedfs", sequence.NewMemorySequencer(), 5*1024*1024*1024, 5, false)
+
+	dc := NewDataCenter("dc1")
+	topo.LinkChildNode(dc)
+	rack := NewRack("rack1")
+	dc.LinkChildNode(rack)
+
+	dn := NewDataNode("server1")
+	rack.LinkChildNode(dn)
+
+	// Server with capacity for exactly 10 volumes
+	disk := NewDisk(types.HardDriveType.String())
+	diskUsage := disk.diskUsages.getOrCreateDisk(types.HardDriveType)
+	diskUsage.maxVolumeCount = 10
+	dn.LinkChildNode(disk)
+
+	// Also set max volume count on the DataNode level (gets propagated up)
+	dn.diskUsages.getOrCreateDisk(types.HardDriveType).maxVolumeCount = 10
+
+	vg := NewDefaultVolumeGrowth()
+	rp, _ := super_block.NewReplicaPlacementFromString("000")
+
+	option := &VolumeGrowOption{
+		Collection:       "test",
+		ReplicaPlacement: rp,
+		DiskType:         types.HardDriveType,
+	}
+
+	// Test accurate capacity reporting at each step
+	for i := 0; i < 10; i++ {
+		// Check available space before reservation
+		availableBefore := dn.AvailableSpaceFor(option)
+		availableForReservation := dn.AvailableSpaceForReservation(option)
+
+		expectedAvailable := int64(10 - i)
+		if availableBefore != expectedAvailable {
+			t.Errorf("Step %d: Expected %d available, got %d", i, expectedAvailable, availableBefore)
+		}
+
+		if availableForReservation != expectedAvailable {
+			t.Errorf("Step %d: Expected %d available for reservation, got %d", i, expectedAvailable, availableForReservation)
+		}
+
+		// Try to reserve and allocate
+		_, reservation, err := vg.findEmptySlotsForOneVolume(topo, option, true)
+		if err != nil {
+			t.Fatalf("Step %d: Unexpected reservation failure: %v", i, err)
+		}
+
+		// Check that available space for reservation decreased
+		availableAfterReservation := dn.AvailableSpaceForReservation(option)
+		if availableAfterReservation != expectedAvailable-1 {
+			t.Errorf("Step %d: Expected %d available after reservation, got %d",
+				i, expectedAvailable-1, availableAfterReservation)
+		}
+
+		// Simulate successful volume creation by properly updating disk usage hierarchy
+		disk := dn.children[NodeId(types.HardDriveType.String())].(*Disk)
+
+		// Create a volume usage delta to simulate volume creation
+		deltaDiskUsage := &DiskUsageCounts{
+			volumeCount: 1,
+		}
+
+		// Properly propagate the usage up the hierarchy
+		disk.UpAdjustDiskUsageDelta(types.HardDriveType, deltaDiskUsage)
+
+		// Debug: Check the volume count after update
+		diskUsageOnNode := dn.diskUsages.getOrCreateDisk(types.HardDriveType)
+		currentVolumeCount := atomic.LoadInt64(&diskUsageOnNode.volumeCount)
+		t.Logf("Step %d: Volume count after update: %d", i, currentVolumeCount)
+
+		// Release reservation
+		reservation.releaseAllReservations()
+
+		// Verify final state
+		availableAfter := dn.AvailableSpaceFor(option)
+		expectedAfter := int64(10 - i - 1)
+		if availableAfter != expectedAfter {
+			t.Errorf("Step %d: Expected %d available after creation, got %d",
+				i, expectedAfter, availableAfter)
+			// More debugging
+			diskUsageOnNode := dn.diskUsages.getOrCreateDisk(types.HardDriveType)
+			maxVolumes := atomic.LoadInt64(&diskUsageOnNode.maxVolumeCount)
+			remoteVolumes := atomic.LoadInt64(&diskUsageOnNode.remoteVolumeCount)
+			actualVolumeCount := atomic.LoadInt64(&diskUsageOnNode.volumeCount)
+			t.Logf("Debug Step %d: max=%d, volume=%d, remote=%d", i, maxVolumes, actualVolumeCount, remoteVolumes)
+		}
+	}
+
+	// At this point, no more reservations should succeed
+	_, _, err := vg.findEmptySlotsForOneVolume(topo, option, true)
+	if err == nil {
+		t.Error("Expected reservation to fail when at capacity")
+	}
+
+	t.Logf("✅ Capacity judgment accuracy test passed")
+}
+
+// TestReservationSystemPerformance measures the performance impact of reservations
+func TestReservationSystemPerformance(t *testing.T) {
+	// Create topology
+	topo := NewTopology("weedfs", sequence.NewMemorySequencer(), 32*1024, 5, false)
+
+	dc := NewDataCenter("dc1")
+	topo.LinkChildNode(dc)
+	rack := NewRack("rack1")
+	dc.LinkChildNode(rack)
+
+	dn := NewDataNode("server1")
+	rack.LinkChildNode(dn)
+
+	disk := NewDisk(types.HardDriveType.String())
+	disk.diskUsages.getOrCreateDisk(types.HardDriveType).maxVolumeCount = 1000
+	dn.LinkChildNode(disk)
+
+	vg := NewDefaultVolumeGrowth()
+	rp, _ := super_block.NewReplicaPlacementFromString("000")
+
+	option := &VolumeGrowOption{
+		Collection:       "test",
+		ReplicaPlacement: rp,
+		DiskType:         types.HardDriveType,
+	}
+
+	// Benchmark reservation operations
+	const iterations = 1000
+
+	startTime := time.Now()
+	for i := 0; i < iterations; i++ {
+		_, reservation, err := vg.findEmptySlotsForOneVolume(topo, option, true)
+		if err != nil {
+			t.Fatalf("Iteration %d failed: %v", i, err)
+		}
+		reservation.releaseAllReservations()
+
+		// Simulate volume creation
+		diskUsage := dn.diskUsages.getOrCreateDisk(types.HardDriveType)
+		atomic.AddInt64(&diskUsage.volumeCount, 1)
+	}
+	duration := time.Since(startTime)
+
+	avgDuration := duration / iterations
+	t.Logf("Performance: %d reservations in %v (avg: %v per reservation)",
+		iterations, duration, avgDuration)
+
+	// Performance should be reasonable (less than 1ms per reservation on average)
+	if avgDuration > time.Millisecond {
+		t.Errorf("Reservation system performance concern: %v per reservation", avgDuration)
+	} else {
+		t.Logf("✅ Performance test passed: %v per reservation", avgDuration)
+	}
+}
diff --git a/weed/topology/rack.go b/weed/topology/rack.go
index d82ef7986..f526cd84d 100644
--- a/weed/topology/rack.go
+++ b/weed/topology/rack.go
@@ -1,12 +1,13 @@
 package topology
 
 import (
-	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
-	"github.com/seaweedfs/seaweedfs/weed/storage/types"
-	"github.com/seaweedfs/seaweedfs/weed/util"
 	"slices"
 	"strings"
 	"time"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
+	"github.com/seaweedfs/seaweedfs/weed/storage/types"
+	"github.com/seaweedfs/seaweedfs/weed/util"
 )
 
 type Rack struct {
@@ -19,6 +20,7 @@ func NewRack(id string) *Rack {
 	r.nodeType = "Rack"
 	r.diskUsages = newDiskUsages()
 	r.children = make(map[NodeId]Node)
+	r.capacityReservations = newCapacityReservations()
 	r.NodeImpl.value = r
 	return r
 }
diff --git a/weed/topology/topology.go b/weed/topology/topology.go
index 750c00ea2..bbae97d72 100644
--- a/weed/topology/topology.go
+++ b/weed/topology/topology.go
@@ -67,6 +67,7 @@ func NewTopology(id string, seq sequence.Sequencer, volumeSizeLimit uint64, puls
 	t.NodeImpl.value = t
 	t.diskUsages = newDiskUsages()
 	t.children = make(map[NodeId]Node)
+	t.capacityReservations = newCapacityReservations()
 	t.collectionMap = util.NewConcurrentReadMap()
 	t.ecShardMap = make(map[needle.VolumeId]*EcShardLocations)
 	t.pulse = int64(pulse)
diff --git a/weed/topology/volume_growth.go b/weed/topology/volume_growth.go
index c62fd72a0..f7af4e0a5 100644
--- a/weed/topology/volume_growth.go
+++ b/weed/topology/volume_growth.go
@@ -74,6 +74,22 @@ type VolumeGrowth struct {
 	accessLock sync.Mutex
 }
 
+// VolumeGrowReservation tracks capacity reservations for a volume creation operation
+type VolumeGrowReservation struct {
+	servers        []*DataNode
+	reservationIds []string
+	diskType       types.DiskType
+}
+
+// releaseAllReservations releases all reservations in this volume grow operation
+func (vgr *VolumeGrowReservation) releaseAllReservations() {
+	for i, server := range vgr.servers {
+		if i < len(vgr.reservationIds) && vgr.reservationIds[i] != "" {
+			server.ReleaseReservedCapacity(vgr.reservationIds[i])
+		}
+	}
+}
+
 func (o *VolumeGrowOption) String() string {
 	blob, _ := json.Marshal(o)
 	return string(blob)
@@ -125,10 +141,17 @@ func (vg *VolumeGrowth) GrowByCountAndType(grpcDialOption grpc.DialOption, targe
 }
 
 func (vg *VolumeGrowth) findAndGrow(grpcDialOption grpc.DialOption, topo *Topology, option *VolumeGrowOption) (result []*master_pb.VolumeLocation, err error) {
-	servers, e := vg.findEmptySlotsForOneVolume(topo, option)
+	servers, reservation, e := vg.findEmptySlotsForOneVolume(topo, option, true) // use reservations
 	if e != nil {
 		return nil, e
 	}
+	// Ensure reservations are released if anything goes wrong
+	defer func() {
+		if err != nil && reservation != nil {
+			reservation.releaseAllReservations()
+		}
+	}()
+
 	for !topo.LastLeaderChangeTime.Add(constants.VolumePulseSeconds * 2).Before(time.Now()) {
 		glog.V(0).Infof("wait for volume servers to join back")
 		time.Sleep(constants.VolumePulseSeconds / 2)
@@ -137,7 +160,7 @@ func (vg *VolumeGrowth) findAndGrow(grpcDialOption grpc.DialOption, topo *Topolo
 	if raftErr != nil {
 		return nil, raftErr
 	}
-	if err = vg.grow(grpcDialOption, topo, vid, option, servers...); err == nil {
+	if err = vg.grow(grpcDialOption, topo, vid, option, reservation, servers...); err == nil {
 		for _, server := range servers {
 			result = append(result, &master_pb.VolumeLocation{
 				Url:        server.Url(),
@@ -156,9 +179,37 @@ func (vg *VolumeGrowth) findAndGrow(grpcDialOption grpc.DialOption, topo *Topolo
 // 2.2 collect all racks that have rp.SameRackCount+1
 // 2.2 collect all data centers that have DiffRackCount+rp.SameRackCount+1
 // 2. find rest data nodes
-func (vg *VolumeGrowth) findEmptySlotsForOneVolume(topo *Topology, option *VolumeGrowOption) (servers []*DataNode, err error) {
+// If useReservations is true, reserves capacity on each server and returns reservation info
+func (vg *VolumeGrowth) findEmptySlotsForOneVolume(topo *Topology, option *VolumeGrowOption, useReservations bool) (servers []*DataNode, reservation *VolumeGrowReservation, err error) {
 	//find main datacenter and other data centers
 	rp := option.ReplicaPlacement
+
+	// Select appropriate functions based on useReservations flag
+	var availableSpaceFunc func(Node, *VolumeGrowOption) int64
+	var reserveOneVolumeFunc func(Node, int64, *VolumeGrowOption) (*DataNode, error)
+
+	if useReservations {
+		availableSpaceFunc = func(node Node, option *VolumeGrowOption) int64 {
+			return node.AvailableSpaceForReservation(option)
+		}
+		reserveOneVolumeFunc = func(node Node, r int64, option *VolumeGrowOption) (*DataNode, error) {
+			return node.ReserveOneVolumeForReservation(r, option)
+		}
+	} else {
+		availableSpaceFunc = func(node Node, option *VolumeGrowOption) int64 {
+			return node.AvailableSpaceFor(option)
+		}
+		reserveOneVolumeFunc = func(node Node, r int64, option *VolumeGrowOption) (*DataNode, error) {
+			return node.ReserveOneVolume(r, option)
+		}
+	}
+
+	// Ensure cleanup of partial reservations on error
+	defer func() {
+		if err != nil && reservation != nil {
+			reservation.releaseAllReservations()
+		}
+	}()
 	mainDataCenter, otherDataCenters, dc_err := topo.PickNodesByWeight(rp.DiffDataCenterCount+1, option, func(node Node) error {
 		if option.DataCenter != "" && node.IsDataCenter() && node.Id() != NodeId(option.DataCenter) {
 			return fmt.Errorf("Not matching preferred data center:%s", option.DataCenter)
@@ -166,14 +217,14 @@ func (vg *VolumeGrowth) findEmptySlotsForOneVolume(topo *Topology, option *Volum
 		if len(node.Children()) < rp.DiffRackCount+1 {
 			return fmt.Errorf("Only has %d racks, not enough for %d.", len(node.Children()), rp.DiffRackCount+1)
 		}
-		if node.AvailableSpaceFor(option) < int64(rp.DiffRackCount+rp.SameRackCount+1) {
-			return fmt.Errorf("Free:%d < Expected:%d", node.AvailableSpaceFor(option), rp.DiffRackCount+rp.SameRackCount+1)
+		if availableSpaceFunc(node, option) < int64(rp.DiffRackCount+rp.SameRackCount+1) {
+			return fmt.Errorf("Free:%d < Expected:%d", availableSpaceFunc(node, option), rp.DiffRackCount+rp.SameRackCount+1)
 		}
 		possibleRacksCount := 0
 		for _, rack := range node.Children() {
 			possibleDataNodesCount := 0
 			for _, n := range rack.Children() {
-				if n.AvailableSpaceFor(option) >= 1 {
+				if availableSpaceFunc(n, option) >= 1 {
 					possibleDataNodesCount++
 				}
 			}
@@ -187,7 +238,7 @@ func (vg *VolumeGrowth) findEmptySlotsForOneVolume(topo *Topology, option *Volum
 		return nil
 	})
 	if dc_err != nil {
-		return nil, dc_err
+		return nil, nil, dc_err
 	}
 
 	//find main rack and other racks
@@ -195,8 +246,8 @@ func (vg *VolumeGrowth) findEmptySlotsForOneVolume(topo *Topology, option *Volum
 		if option.Rack != "" && node.IsRack() && node.Id() != NodeId(option.Rack) {
 			return fmt.Errorf("Not matching preferred rack:%s", option.Rack)
 		}
-		if node.AvailableSpaceFor(option) < int64(rp.SameRackCount+1) {
-			return fmt.Errorf("Free:%d < Expected:%d", node.AvailableSpaceFor(option), rp.SameRackCount+1)
+		if availableSpaceFunc(node, option) < int64(rp.SameRackCount+1) {
+			return fmt.Errorf("Free:%d < Expected:%d", availableSpaceFunc(node, option), rp.SameRackCount+1)
 		}
 		if len(node.Children()) < rp.SameRackCount+1 {
 			// a bit faster way to test free racks
@@ -204,7 +255,7 @@ func (vg *VolumeGrowth) findEmptySlotsForOneVolume(topo *Topology, option *Volum
 		}
 		possibleDataNodesCount := 0
 		for _, n := range node.Children() {
-			if n.AvailableSpaceFor(option) >= 1 {
+			if availableSpaceFunc(n, option) >= 1 {
 				possibleDataNodesCount++
 			}
 		}
@@ -214,7 +265,7 @@ func (vg *VolumeGrowth) findEmptySlotsForOneVolume(topo *Topology, option *Volum
 		return nil
 	})
 	if rackErr != nil {
-		return nil, rackErr
+		return nil, nil, rackErr
 	}
 
 	//find main server and other servers
@@ -222,13 +273,13 @@ func (vg *VolumeGrowth) findEmptySlotsForOneVolume(topo *Topology, option *Volum
 		if option.DataNode != "" && node.IsDataNode() && node.Id() != NodeId(option.DataNode) {
 			return fmt.Errorf("Not matching preferred data node:%s", option.DataNode)
 		}
-		if node.AvailableSpaceFor(option) < 1 {
-			return fmt.Errorf("Free:%d < Expected:%d", node.AvailableSpaceFor(option), 1)
+		if availableSpaceFunc(node, option) < 1 {
+			return fmt.Errorf("Free:%d < Expected:%d", availableSpaceFunc(node, option), 1)
 		}
 		return nil
 	})
 	if serverErr != nil {
-		return nil, serverErr
+		return nil, nil, serverErr
 	}
 
 	servers = append(servers, mainServer.(*DataNode))
@@ -236,25 +287,47 @@ func (vg *VolumeGrowth) findEmptySlotsForOneVolume(topo *Topology, option *Volum
 		servers = append(servers, server.(*DataNode))
 	}
 	for _, rack := range otherRacks {
-		r := rand.Int64N(rack.AvailableSpaceFor(option))
-		if server, e := rack.ReserveOneVolume(r, option); e == nil {
+		r := rand.Int64N(availableSpaceFunc(rack, option))
+		if server, e := reserveOneVolumeFunc(rack, r, option); e == nil {
 			servers = append(servers, server)
 		} else {
-			return servers, e
+			return servers, nil, e
 		}
 	}
 	for _, datacenter := range otherDataCenters {
-		r := rand.Int64N(datacenter.AvailableSpaceFor(option))
-		if server, e := datacenter.ReserveOneVolume(r, option); e == nil {
+		r := rand.Int64N(availableSpaceFunc(datacenter, option))
+		if server, e := reserveOneVolumeFunc(datacenter, r, option); e == nil {
 			servers = append(servers, server)
 		} else {
-			return servers, e
+			return servers, nil, e
 		}
 	}
-	return
+
+	// If reservations are requested, try to reserve capacity on each server
+	if useReservations {
+		reservation = &VolumeGrowReservation{
+			servers:        servers,
+			reservationIds: make([]string, len(servers)),
+			diskType:       option.DiskType,
+		}
+
+		// Try to reserve capacity on each server
+		for i, server := range servers {
+			reservationId, success := server.TryReserveCapacity(option.DiskType, 1)
+			if !success {
+				return servers, nil, fmt.Errorf("failed to reserve capacity on server %s", server.Id())
+			}
+			reservation.reservationIds[i] = reservationId
+		}
+
+		glog.V(1).Infof("Successfully reserved capacity on %d servers for volume creation", len(servers))
+	}
+
+	return servers, reservation, nil
 }
 
-func (vg *VolumeGrowth) grow(grpcDialOption grpc.DialOption, topo *Topology, vid needle.VolumeId, option *VolumeGrowOption, servers ...*DataNode) (growErr error) {
+// grow creates volumes on the provided servers, optionally managing capacity reservations
+func (vg *VolumeGrowth) grow(grpcDialOption grpc.DialOption, topo *Topology, vid needle.VolumeId, option *VolumeGrowOption, reservation *VolumeGrowReservation, servers ...*DataNode) (growErr error) {
 	var createdVolumes []storage.VolumeInfo
 	for _, server := range servers {
 		if err := AllocateVolume(server, grpcDialOption, vid, option); err == nil {
@@ -283,6 +356,10 @@ func (vg *VolumeGrowth) grow(grpcDialOption grpc.DialOption, topo *Topology, vid
 			topo.RegisterVolumeLayout(vi, server)
 			glog.V(0).Infof("Registered Volume %d on %s", vid, server.NodeImpl.String())
 		}
+		// Release reservations on success since volumes are now registered
+		if reservation != nil {
+			reservation.releaseAllReservations()
+		}
 	} else {
 		// cleaning up created volume replicas
 		for i, vi := range createdVolumes {
@@ -291,6 +368,7 @@ func (vg *VolumeGrowth) grow(grpcDialOption grpc.DialOption, topo *Topology, vid
 				glog.Warningf("Failed to clean up volume %d on %s", vid, server.NodeImpl.String())
 			}
 		}
+		// Reservations will be released by the caller in case of failure
 	}
 
 	return growErr
diff --git a/weed/topology/volume_growth_reservation_test.go b/weed/topology/volume_growth_reservation_test.go
new file mode 100644
index 000000000..7b06e626d
--- /dev/null
+++ b/weed/topology/volume_growth_reservation_test.go
@@ -0,0 +1,276 @@
+package topology
+
+import (
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/seaweedfs/seaweedfs/weed/sequence"
+	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
+	"github.com/seaweedfs/seaweedfs/weed/storage/super_block"
+	"github.com/seaweedfs/seaweedfs/weed/storage/types"
+)
+
+// MockGrpcDialOption simulates grpc connection for testing
+type MockGrpcDialOption struct{}
+
+// simulateVolumeAllocation mocks the volume allocation process
+func simulateVolumeAllocation(server *DataNode, vid needle.VolumeId, option *VolumeGrowOption) error {
+	// Simulate some processing time
+	time.Sleep(time.Millisecond * 10)
+	return nil
+}
+
+func TestVolumeGrowth_ReservationBasedAllocation(t *testing.T) {
+	// Create test topology with single server for predictable behavior
+	topo := NewTopology("weedfs", sequence.NewMemorySequencer(), 32*1024, 5, false)
+
+	// Create data center and rack
+	dc := NewDataCenter("dc1")
+	topo.LinkChildNode(dc)
+	rack := NewRack("rack1")
+	dc.LinkChildNode(rack)
+
+	// Create single data node with limited capacity
+	dn := NewDataNode("server1")
+	rack.LinkChildNode(dn)
+
+	// Set up disk with limited capacity (only 5 volumes)
+	disk := NewDisk(types.HardDriveType.String())
+	disk.diskUsages.getOrCreateDisk(types.HardDriveType).maxVolumeCount = 5
+	dn.LinkChildNode(disk)
+
+	// Test volume growth with reservation
+	vg := NewDefaultVolumeGrowth()
+	rp, _ := super_block.NewReplicaPlacementFromString("000") // Single copy (no replicas)
+
+	option := &VolumeGrowOption{
+		Collection:       "test",
+		ReplicaPlacement: rp,
+		DiskType:         types.HardDriveType,
+	}
+
+	// Try to create volumes and verify reservations work
+	for i := 0; i < 5; i++ {
+		servers, reservation, err := vg.findEmptySlotsForOneVolume(topo, option, true)
+		if err != nil {
+			t.Errorf("Failed to find slots with reservation on iteration %d: %v", i, err)
+			continue
+		}
+
+		if len(servers) != 1 {
+			t.Errorf("Expected 1 server for replica placement 000, got %d", len(servers))
+		}
+
+		if len(reservation.reservationIds) != 1 {
+			t.Errorf("Expected 1 reservation ID, got %d", len(reservation.reservationIds))
+		}
+
+		// Verify the reservation is on our expected server
+		server := servers[0]
+		if server != dn {
+			t.Errorf("Expected volume to be allocated on server1, got %s", server.Id())
+		}
+
+		// Check available space before and after reservation
+		availableBeforeCreation := server.AvailableSpaceFor(option)
+		expectedBefore := int64(5 - i)
+		if availableBeforeCreation != expectedBefore {
+			t.Errorf("Iteration %d: Expected %d base available space, got %d", i, expectedBefore, availableBeforeCreation)
+		}
+
+		// Simulate successful volume creation
+		disk := dn.children[NodeId(types.HardDriveType.String())].(*Disk)
+		deltaDiskUsage := &DiskUsageCounts{
+			volumeCount: 1,
+		}
+		disk.UpAdjustDiskUsageDelta(types.HardDriveType, deltaDiskUsage)
+
+		// Release reservation after successful creation
+		reservation.releaseAllReservations()
+
+		// Verify available space after creation
+		availableAfterCreation := server.AvailableSpaceFor(option)
+		expectedAfter := int64(5 - i - 1)
+		if availableAfterCreation != expectedAfter {
+			t.Errorf("Iteration %d: Expected %d available space after creation, got %d", i, expectedAfter, availableAfterCreation)
+		}
+	}
+
+	// After 5 volumes, should have no more capacity
+	_, _, err := vg.findEmptySlotsForOneVolume(topo, option, true)
+	if err == nil {
+		t.Error("Expected volume allocation to fail when server is at capacity")
+	}
+}
+
+func TestVolumeGrowth_ConcurrentAllocationPreventsRaceCondition(t *testing.T) {
+	// Create test topology with very limited capacity
+	topo := NewTopology("weedfs", sequence.NewMemorySequencer(), 32*1024, 5, false)
+
+	dc := NewDataCenter("dc1")
+	topo.LinkChildNode(dc)
+	rack := NewRack("rack1")
+	dc.LinkChildNode(rack)
+
+	// Single data node with capacity for only 5 volumes
+	dn := NewDataNode("server1")
+	rack.LinkChildNode(dn)
+
+	disk := NewDisk(types.HardDriveType.String())
+	disk.diskUsages.getOrCreateDisk(types.HardDriveType).maxVolumeCount = 5
+	dn.LinkChildNode(disk)
+
+	vg := NewDefaultVolumeGrowth()
+	rp, _ := super_block.NewReplicaPlacementFromString("000") // Single copy (no replicas)
+
+	option := &VolumeGrowOption{
+		Collection:       "test",
+		ReplicaPlacement: rp,
+		DiskType:         types.HardDriveType,
+	}
+
+	// Simulate concurrent volume creation attempts
+	const concurrentRequests = 10
+	var wg sync.WaitGroup
+	var successCount, failureCount atomic.Int32
+
+	for i := 0; i < concurrentRequests; i++ {
+		wg.Add(1)
+		go func(requestId int) {
+			defer wg.Done()
+
+			_, reservation, err := vg.findEmptySlotsForOneVolume(topo, option, true)
+
+			if err != nil {
+				failureCount.Add(1)
+				t.Logf("Request %d failed as expected: %v", requestId, err)
+			} else {
+				successCount.Add(1)
+				t.Logf("Request %d succeeded, got reservation", requestId)
+
+				// Release the reservation to simulate completion
+				if reservation != nil {
+					reservation.releaseAllReservations()
+					// Simulate volume creation by incrementing count
+					disk := dn.children[NodeId(types.HardDriveType.String())].(*Disk)
+					deltaDiskUsage := &DiskUsageCounts{
+						volumeCount: 1,
+					}
+					disk.UpAdjustDiskUsageDelta(types.HardDriveType, deltaDiskUsage)
+				}
+			}
+		}(i)
+	}
+
+	wg.Wait()
+
+	// With reservation system, only 5 requests should succeed (capacity limit)
+	// The rest should fail due to insufficient capacity
+	if successCount.Load() != 5 {
+		t.Errorf("Expected exactly 5 successful reservations, got %d", successCount.Load())
+	}
+
+	if failureCount.Load() != 5 {
+		t.Errorf("Expected exactly 5 failed reservations, got %d", failureCount.Load())
+	}
+
+	// Verify final state
+	finalAvailable := dn.AvailableSpaceFor(option)
+	if finalAvailable != 0 {
+		t.Errorf("Expected 0 available space after all allocations, got %d", finalAvailable)
+	}
+
+	t.Logf("Concurrent test completed: %d successes, %d failures", successCount.Load(), failureCount.Load())
+}
+
+func TestVolumeGrowth_ReservationFailureRollback(t *testing.T) {
+	// Create topology with multiple servers, but limited total capacity
+	topo := NewTopology("weedfs", sequence.NewMemorySequencer(), 32*1024, 5, false)
+
+	dc := NewDataCenter("dc1")
+	topo.LinkChildNode(dc)
+	rack := NewRack("rack1")
+	dc.LinkChildNode(rack)
+
+	// Create two servers with different available capacity
+	dn1 := NewDataNode("server1")
+	dn2 := NewDataNode("server2")
+	rack.LinkChildNode(dn1)
+	rack.LinkChildNode(dn2)
+
+	// Server 1: 5 available slots
+	disk1 := NewDisk(types.HardDriveType.String())
+	disk1.diskUsages.getOrCreateDisk(types.HardDriveType).maxVolumeCount = 5
+	dn1.LinkChildNode(disk1)
+
+	// Server 2: 0 available slots (full)
+	disk2 := NewDisk(types.HardDriveType.String())
+	diskUsage2 := disk2.diskUsages.getOrCreateDisk(types.HardDriveType)
+	diskUsage2.maxVolumeCount = 5
+	diskUsage2.volumeCount = 5
+	dn2.LinkChildNode(disk2)
+
+	vg := NewDefaultVolumeGrowth()
+	rp, _ := super_block.NewReplicaPlacementFromString("010") // requires 2 replicas
+
+	option := &VolumeGrowOption{
+		Collection:       "test",
+		ReplicaPlacement: rp,
+		DiskType:         types.HardDriveType,
+	}
+
+	// This should fail because we can't satisfy replica requirements
+	// (need 2 servers but only 1 has space)
+	_, _, err := vg.findEmptySlotsForOneVolume(topo, option, true)
+	if err == nil {
+		t.Error("Expected reservation to fail due to insufficient replica capacity")
+	}
+
+	// Verify no reservations are left hanging
+	available1 := dn1.AvailableSpaceForReservation(option)
+	if available1 != 5 {
+		t.Errorf("Expected server1 to have all capacity available after failed reservation, got %d", available1)
+	}
+
+	available2 := dn2.AvailableSpaceForReservation(option)
+	if available2 != 0 {
+		t.Errorf("Expected server2 to have no capacity available, got %d", available2)
+	}
+}
+
+func TestVolumeGrowth_ReservationTimeout(t *testing.T) {
+	dn := NewDataNode("server1")
+	diskType := types.HardDriveType
+
+	// Set up capacity
+	diskUsage := dn.diskUsages.getOrCreateDisk(diskType)
+	diskUsage.maxVolumeCount = 5
+
+	// Create a reservation
+	reservationId, success := dn.TryReserveCapacity(diskType, 2)
+	if !success {
+		t.Fatal("Expected successful reservation")
+	}
+
+	// Manually set the reservation time to simulate old reservation
+	dn.capacityReservations.Lock()
+	if reservation, exists := dn.capacityReservations.reservations[reservationId]; exists {
+		reservation.createdAt = time.Now().Add(-10 * time.Minute)
+	}
+	dn.capacityReservations.Unlock()
+
+	// Try another reservation - this should trigger cleanup and succeed
+	_, success = dn.TryReserveCapacity(diskType, 3)
+	if !success {
+		t.Error("Expected reservation to succeed after cleanup of expired reservation")
+	}
+
+	// Original reservation should be cleaned up
+	option := &VolumeGrowOption{DiskType: diskType}
+	available := dn.AvailableSpaceForReservation(option)
+	if available != 2 { // 5 - 3 = 2
+		t.Errorf("Expected 2 available slots after cleanup and new reservation, got %d", available)
+	}
+}
diff --git a/weed/topology/volume_growth_test.go b/weed/topology/volume_growth_test.go
index 286289148..9bf3f3747 100644
--- a/weed/topology/volume_growth_test.go
+++ b/weed/topology/volume_growth_test.go
@@ -145,7 +145,7 @@ func TestFindEmptySlotsForOneVolume(t *testing.T) {
 		Rack:             "",
 		DataNode:         "",
 	}
-	servers, err := vg.findEmptySlotsForOneVolume(topo, volumeGrowOption)
+	servers, _, err := vg.findEmptySlotsForOneVolume(topo, volumeGrowOption, false)
 	if err != nil {
 		fmt.Println("finding empty slots error :", err)
 		t.Fail()
@@ -267,7 +267,7 @@ func TestReplication011(t *testing.T) {
 		Rack:             "",
 		DataNode:         "",
 	}
-	servers, err := vg.findEmptySlotsForOneVolume(topo, volumeGrowOption)
+	servers, _, err := vg.findEmptySlotsForOneVolume(topo, volumeGrowOption, false)
 	if err != nil {
 		fmt.Println("finding empty slots error :", err)
 		t.Fail()
@@ -345,7 +345,7 @@ func TestFindEmptySlotsForOneVolumeScheduleByWeight(t *testing.T) {
 	distribution := map[NodeId]int{}
 	// assign 1000 volumes
 	for i := 0; i < 1000; i++ {
-		servers, err := vg.findEmptySlotsForOneVolume(topo, volumeGrowOption)
+		servers, _, err := vg.findEmptySlotsForOneVolume(topo, volumeGrowOption, false)
 		if err != nil {
 			fmt.Println("finding empty slots error :", err)
 			t.Fail()