1 files changed, 420 insertions, 0 deletions
diff --git a/weed/storage/erasure_coding/placement/placement.go b/weed/storage/erasure_coding/placement/placement.go
new file mode 100644
index 000000000..67e21c1f8
--- /dev/null
+++ b/weed/storage/erasure_coding/placement/placement.go
@@ -0,0 +1,420 @@
+// Package placement provides consolidated EC shard placement logic used by
+// both shell commands and worker tasks.
+//
+// This package encapsulates the algorithms for:
+// - Selecting destination nodes/disks for EC shards
+// - Ensuring proper spread across racks, servers, and disks
+// - Balancing shards across the cluster
+package placement
+
+import (
+	"fmt"
+	"sort"
+)
+
+// DiskCandidate represents a disk that can receive EC shards
+type DiskCandidate struct {
+	NodeID     string
+	DiskID     uint32
+	DataCenter string
+	Rack       string
+
+	// Capacity information
+	VolumeCount    int64
+	MaxVolumeCount int64
+	ShardCount     int // Current number of EC shards on this disk
+	FreeSlots      int // Available slots for new shards
+
+	// Load information
+	LoadCount int // Number of active tasks on this disk
+}
+
+// NodeCandidate represents a server node that can receive EC shards
+type NodeCandidate struct {
+	NodeID     string
+	DataCenter string
+	Rack       string
+	FreeSlots  int
+	ShardCount int              // Total shards across all disks
+	Disks      []*DiskCandidate // All disks on this node
+}
+
+// PlacementRequest configures EC shard placement behavior
+type PlacementRequest struct {
+	// ShardsNeeded is the total number of shards to place
+	ShardsNeeded int
+
+	// MaxShardsPerServer limits how many shards can be placed on a single server
+	// 0 means no limit (but prefer spreading when possible)
+	MaxShardsPerServer int
+
+	// MaxShardsPerRack limits how many shards can be placed in a single rack
+	// 0 means no limit
+	MaxShardsPerRack int
+
+	// MaxTaskLoad is the maximum task load count for a disk to be considered
+	MaxTaskLoad int
+
+	// PreferDifferentServers when true, spreads shards across different servers
+	// before using multiple disks on the same server
+	PreferDifferentServers bool
+
+	// PreferDifferentRacks when true, spreads shards across different racks
+	// before using multiple servers in the same rack
+	PreferDifferentRacks bool
+}
+
+// DefaultPlacementRequest returns the default placement configuration
+func DefaultPlacementRequest() PlacementRequest {
+	return PlacementRequest{
+		ShardsNeeded:           14,
+		MaxShardsPerServer:     0,
+		MaxShardsPerRack:       0,
+		MaxTaskLoad:            5,
+		PreferDifferentServers: true,
+		PreferDifferentRacks:   true,
+	}
+}
+
+// PlacementResult contains the selected destinations for EC shards
+type PlacementResult struct {
+	SelectedDisks []*DiskCandidate
+
+	// Statistics
+	ServersUsed int
+	RacksUsed   int
+	DCsUsed     int
+
+	// Distribution maps
+	ShardsPerServer map[string]int
+	ShardsPerRack   map[string]int
+	ShardsPerDC     map[string]int
+}
+
+// SelectDestinations selects the best disks for EC shard placement.
+// This is the main entry point for EC placement logic.
+//
+// The algorithm works in multiple passes:
+// 1. First pass: Select one disk from each rack (maximize rack diversity)
+// 2. Second pass: Select one disk from each unused server in used racks (maximize server diversity)
+// 3. Third pass: Select additional disks from servers already used (maximize disk diversity)
+func SelectDestinations(disks []*DiskCandidate, config PlacementRequest) (*PlacementResult, error) {
+	if len(disks) == 0 {
+		return nil, fmt.Errorf("no disk candidates provided")
+	}
+	if config.ShardsNeeded <= 0 {
+		return nil, fmt.Errorf("shardsNeeded must be positive, got %d", config.ShardsNeeded)
+	}
+
+	// Filter suitable disks
+	suitable := filterSuitableDisks(disks, config)
+	if len(suitable) == 0 {
+		return nil, fmt.Errorf("no suitable disks found after filtering")
+	}
+
+	// Build indexes for efficient lookup
+	rackToDisks := groupDisksByRack(suitable)
+
+	result := &PlacementResult{
+		SelectedDisks:   make([]*DiskCandidate, 0, config.ShardsNeeded),
+		ShardsPerServer: make(map[string]int),
+		ShardsPerRack:   make(map[string]int),
+		ShardsPerDC:     make(map[string]int),
+	}
+
+	usedDisks := make(map[string]bool)   // "nodeID:diskID" -> bool
+	usedServers := make(map[string]bool) // nodeID -> bool
+	usedRacks := make(map[string]bool)   // "dc:rack" -> bool
+
+	// Pass 1: Select one disk from each rack (maximize rack diversity)
+	if config.PreferDifferentRacks {
+		// Sort racks by number of available servers (descending) to prioritize racks with more options
+		sortedRacks := sortRacksByServerCount(rackToDisks)
+		for _, rackKey := range sortedRacks {
+			if len(result.SelectedDisks) >= config.ShardsNeeded {
+				break
+			}
+			rackDisks := rackToDisks[rackKey]
+			// Select best disk from this rack, preferring a new server
+			disk := selectBestDiskFromRack(rackDisks, usedServers, usedDisks, config)
+			if disk != nil {
+				addDiskToResult(result, disk, usedDisks, usedServers, usedRacks)
+			}
+		}
+	}
+
+	// Pass 2: Select disks from unused servers in already-used racks
+	if config.PreferDifferentServers && len(result.SelectedDisks) < config.ShardsNeeded {
+		for _, rackKey := range getSortedRackKeys(rackToDisks) {
+			if len(result.SelectedDisks) >= config.ShardsNeeded {
+				break
+			}
+			rackDisks := rackToDisks[rackKey]
+			for _, disk := range sortDisksByScore(rackDisks) {
+				if len(result.SelectedDisks) >= config.ShardsNeeded {
+					break
+				}
+				diskKey := getDiskKey(disk)
+				if usedDisks[diskKey] {
+					continue
+				}
+				// Skip if server already used (we want different servers in this pass)
+				if usedServers[disk.NodeID] {
+					continue
+				}
+				// Check server limit
+				if config.MaxShardsPerServer > 0 && result.ShardsPerServer[disk.NodeID] >= config.MaxShardsPerServer {
+					continue
+				}
+				// Check rack limit
+				if config.MaxShardsPerRack > 0 && result.ShardsPerRack[getRackKey(disk)] >= config.MaxShardsPerRack {
+					continue
+				}
+				addDiskToResult(result, disk, usedDisks, usedServers, usedRacks)
+			}
+		}
+	}
+
+	// Pass 3: Fill remaining slots from already-used servers (different disks)
+	// Use round-robin across servers to balance shards evenly
+	if len(result.SelectedDisks) < config.ShardsNeeded {
+		// Group remaining disks by server
+		serverToRemainingDisks := make(map[string][]*DiskCandidate)
+		for _, disk := range suitable {
+			if !usedDisks[getDiskKey(disk)] {
+				serverToRemainingDisks[disk.NodeID] = append(serverToRemainingDisks[disk.NodeID], disk)
+			}
+		}
+
+		// Sort each server's disks by score
+		for serverID := range serverToRemainingDisks {
+			serverToRemainingDisks[serverID] = sortDisksByScore(serverToRemainingDisks[serverID])
+		}
+
+		// Round-robin: repeatedly select from the server with the fewest shards
+		for len(result.SelectedDisks) < config.ShardsNeeded {
+			// Find server with fewest shards that still has available disks
+			var bestServer string
+			minShards := -1
+			for serverID, disks := range serverToRemainingDisks {
+				if len(disks) == 0 {
+					continue
+				}
+				// Check server limit
+				if config.MaxShardsPerServer > 0 && result.ShardsPerServer[serverID] >= config.MaxShardsPerServer {
+					continue
+				}
+				shardCount := result.ShardsPerServer[serverID]
+				if minShards == -1 || shardCount < minShards {
+					minShards = shardCount
+					bestServer = serverID
+				} else if shardCount == minShards && serverID < bestServer {
+					// Tie-break by server name for determinism
+					bestServer = serverID
+				}
+			}
+
+			if bestServer == "" {
+				// No more servers with available disks
+				break
+			}
+
+			// Pop the best disk from this server
+			disks := serverToRemainingDisks[bestServer]
+			disk := disks[0]
+			serverToRemainingDisks[bestServer] = disks[1:]
+
+			// Check rack limit
+			if config.MaxShardsPerRack > 0 && result.ShardsPerRack[getRackKey(disk)] >= config.MaxShardsPerRack {
+				continue
+			}
+
+			addDiskToResult(result, disk, usedDisks, usedServers, usedRacks)
+		}
+	}
+
+	// Calculate final statistics
+	result.ServersUsed = len(usedServers)
+	result.RacksUsed = len(usedRacks)
+	dcSet := make(map[string]bool)
+	for _, disk := range result.SelectedDisks {
+		dcSet[disk.DataCenter] = true
+	}
+	result.DCsUsed = len(dcSet)
+
+	return result, nil
+}
+
+// filterSuitableDisks filters disks that are suitable for EC placement
+func filterSuitableDisks(disks []*DiskCandidate, config PlacementRequest) []*DiskCandidate {
+	var suitable []*DiskCandidate
+	for _, disk := range disks {
+		if disk.FreeSlots <= 0 {
+			continue
+		}
+		if config.MaxTaskLoad > 0 && disk.LoadCount > config.MaxTaskLoad {
+			continue
+		}
+		suitable = append(suitable, disk)
+	}
+	return suitable
+}
+
+// groupDisksByRack groups disks by their rack (dc:rack key)
+func groupDisksByRack(disks []*DiskCandidate) map[string][]*DiskCandidate {
+	result := make(map[string][]*DiskCandidate)
+	for _, disk := range disks {
+		key := getRackKey(disk)
+		result[key] = append(result[key], disk)
+	}
+	return result
+}
+
+// groupDisksByServer groups disks by their server
+func groupDisksByServer(disks []*DiskCandidate) map[string][]*DiskCandidate {
+	result := make(map[string][]*DiskCandidate)
+	for _, disk := range disks {
+		result[disk.NodeID] = append(result[disk.NodeID], disk)
+	}
+	return result
+}
+
+// getRackKey returns the unique key for a rack (dc:rack)
+func getRackKey(disk *DiskCandidate) string {
+	return fmt.Sprintf("%s:%s", disk.DataCenter, disk.Rack)
+}
+
+// getDiskKey returns the unique key for a disk (nodeID:diskID)
+func getDiskKey(disk *DiskCandidate) string {
+	return fmt.Sprintf("%s:%d", disk.NodeID, disk.DiskID)
+}
+
+// sortRacksByServerCount returns rack keys sorted by number of servers (ascending)
+func sortRacksByServerCount(rackToDisks map[string][]*DiskCandidate) []string {
+	// Count unique servers per rack
+	rackServerCount := make(map[string]int)
+	for rackKey, disks := range rackToDisks {
+		servers := make(map[string]bool)
+		for _, disk := range disks {
+			servers[disk.NodeID] = true
+		}
+		rackServerCount[rackKey] = len(servers)
+	}
+
+	keys := getSortedRackKeys(rackToDisks)
+	sort.Slice(keys, func(i, j int) bool {
+		// Sort by server count (descending) to pick from racks with more options first
+		return rackServerCount[keys[i]] > rackServerCount[keys[j]]
+	})
+	return keys
+}
+
+// getSortedRackKeys returns rack keys in a deterministic order
+func getSortedRackKeys(rackToDisks map[string][]*DiskCandidate) []string {
+	keys := make([]string, 0, len(rackToDisks))
+	for k := range rackToDisks {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	return keys
+}
+
+// selectBestDiskFromRack selects the best disk from a rack for EC placement
+// It prefers servers that haven't been used yet
+func selectBestDiskFromRack(disks []*DiskCandidate, usedServers, usedDisks map[string]bool, config PlacementRequest) *DiskCandidate {
+	var bestDisk *DiskCandidate
+	bestScore := -1.0
+	bestIsFromUnusedServer := false
+
+	for _, disk := range disks {
+		if usedDisks[getDiskKey(disk)] {
+			continue
+		}
+		isFromUnusedServer := !usedServers[disk.NodeID]
+		score := calculateDiskScore(disk)
+
+		// Prefer unused servers
+		if isFromUnusedServer && !bestIsFromUnusedServer {
+			bestDisk = disk
+			bestScore = score
+			bestIsFromUnusedServer = true
+		} else if isFromUnusedServer == bestIsFromUnusedServer && score > bestScore {
+			bestDisk = disk
+			bestScore = score
+		}
+	}
+
+	return bestDisk
+}
+
+// sortDisksByScore returns disks sorted by score (best first)
+func sortDisksByScore(disks []*DiskCandidate) []*DiskCandidate {
+	sorted := make([]*DiskCandidate, len(disks))
+	copy(sorted, disks)
+	sort.Slice(sorted, func(i, j int) bool {
+		return calculateDiskScore(sorted[i]) > calculateDiskScore(sorted[j])
+	})
+	return sorted
+}
+
+// calculateDiskScore calculates a score for a disk candidate
+// Higher score is better
+func calculateDiskScore(disk *DiskCandidate) float64 {
+	score := 0.0
+
+	// Primary factor: available capacity (lower utilization is better)
+	if disk.MaxVolumeCount > 0 {
+		utilization := float64(disk.VolumeCount) / float64(disk.MaxVolumeCount)
+		score += (1.0 - utilization) * 60.0 // Up to 60 points
+	} else {
+		score += 30.0 // Default if no max count
+	}
+
+	// Secondary factor: fewer shards already on this disk is better
+	score += float64(10-disk.ShardCount) * 2.0 // Up to 20 points
+
+	// Tertiary factor: lower load is better
+	score += float64(10 - disk.LoadCount) // Up to 10 points
+
+	return score
+}
+
+// addDiskToResult adds a disk to the result and updates tracking maps
+func addDiskToResult(result *PlacementResult, disk *DiskCandidate,
+	usedDisks, usedServers, usedRacks map[string]bool) {
+	diskKey := getDiskKey(disk)
+	rackKey := getRackKey(disk)
+
+	result.SelectedDisks = append(result.SelectedDisks, disk)
+	usedDisks[diskKey] = true
+	usedServers[disk.NodeID] = true
+	usedRacks[rackKey] = true
+	result.ShardsPerServer[disk.NodeID]++
+	result.ShardsPerRack[rackKey]++
+	result.ShardsPerDC[disk.DataCenter]++
+}
+
+// VerifySpread checks if the placement result meets diversity requirements
+func VerifySpread(result *PlacementResult, minServers, minRacks int) error {
+	if result.ServersUsed < minServers {
+		return fmt.Errorf("only %d servers used, need at least %d", result.ServersUsed, minServers)
+	}
+	if result.RacksUsed < minRacks {
+		return fmt.Errorf("only %d racks used, need at least %d", result.RacksUsed, minRacks)
+	}
+	return nil
+}
+
+// CalculateIdealDistribution returns the ideal number of shards per server
+// when we have a certain number of shards and servers
+func CalculateIdealDistribution(totalShards, numServers int) (min, max int) {
+	if numServers <= 0 {
+		return 0, totalShards
+	}
+	min = totalShards / numServers
+	max = min
+	if totalShards%numServers != 0 {
+		max = min + 1
+	}
+	return
+}