Implement volume-aware task conflict checking

MAJOR IMPROVEMENT: Tasks now conflict by volume ID, not globally by task type

Changes:
- PRIMARY RULE: Tasks on the same volume ID always conflict (prevents race conditions)
- SECONDARY RULE: Minimal global task type conflicts (currently none)
- Add isDiskAvailableForVolume() for volume-specific availability checking
- Add GetAvailableDisksForVolume() and GetDisksWithEffectiveCapacityForVolume()
- Remove overly restrictive global task type conflicts
- Update planning functions to focus on capacity, not conflicts

Benefits:
✅ Multiple vacuum tasks can run on different volumes simultaneously
✅ Balance and erasure coding can run on different volumes
✅ Still prevents dangerous concurrent operations on same volume
✅ Much more efficient resource utilization
✅ Maintains data integrity and prevents race conditions

This addresses the user feedback that task conflicts should be volume-specific,
not global task type restrictions.

weed/admin/topology/capacity.go

@@ -227,13 +227,9 @@ func (at *ActiveTopology) isDiskAvailableForPlanning(disk *activeDisk, taskType
 		return false
 	}
 
-	// Check for conflicting task types in active tasks only
-	for _, task := range disk.assignedTasks {
-		if at.areTaskTypesConflicting(task.TaskType, taskType) {
-			return false
-		}
-	}
-
+	// For planning purposes, we only check capacity constraints
+	// Volume-specific conflicts will be checked when the actual task is scheduled
+	// with knowledge of the specific volume ID
 	return true
 }
 
@@ -298,3 +294,52 @@ func (at *ActiveTopology) getEffectiveAvailableCapacityUnsafe(disk *activeDisk)
 		ShardSlots:  -netImpact.ShardSlots, // Available shard capacity (negative impact becomes positive availability)
 	}
 }
+
+// GetDisksWithEffectiveCapacityForVolume returns disks with effective capacity for a specific volume
+// Uses volume-aware conflict checking to prevent race conditions on the same volume
+func (at *ActiveTopology) GetDisksWithEffectiveCapacityForVolume(taskType TaskType, volumeID uint32, excludeNodeID string, minCapacity int64) []*DiskInfo {
+	at.mutex.RLock()
+	defer at.mutex.RUnlock()
+
+	var available []*DiskInfo
+
+	for _, disk := range at.disks {
+		if disk.NodeID == excludeNodeID {
+			continue // Skip excluded node
+		}
+
+		if at.isDiskAvailableForVolume(disk, taskType, volumeID) {
+			effectiveCapacity := at.getEffectiveAvailableCapacityUnsafe(disk)
+
+			// Only include disks that meet minimum capacity requirement
+			if int64(effectiveCapacity.VolumeSlots) >= minCapacity {
+				// Create a new DiskInfo with current capacity information
+				diskCopy := DiskInfo{
+					NodeID:     disk.DiskInfo.NodeID,
+					DiskID:     disk.DiskInfo.DiskID,
+					DiskType:   disk.DiskInfo.DiskType,
+					DataCenter: disk.DiskInfo.DataCenter,
+					Rack:       disk.DiskInfo.Rack,
+					LoadCount:  len(disk.pendingTasks) + len(disk.assignedTasks), // Count all tasks
+				}
+
+				// Create a new protobuf DiskInfo to avoid modifying the original
+				diskInfoCopy := &master_pb.DiskInfo{
+					DiskId:            disk.DiskInfo.DiskInfo.DiskId,
+					MaxVolumeCount:    disk.DiskInfo.DiskInfo.MaxVolumeCount,
+					VolumeCount:       disk.DiskInfo.DiskInfo.MaxVolumeCount - int64(effectiveCapacity.VolumeSlots),
+					VolumeInfos:       disk.DiskInfo.DiskInfo.VolumeInfos,
+					EcShardInfos:      disk.DiskInfo.DiskInfo.EcShardInfos,
+					RemoteVolumeCount: disk.DiskInfo.DiskInfo.RemoteVolumeCount,
+					ActiveVolumeCount: disk.DiskInfo.DiskInfo.ActiveVolumeCount,
+					FreeVolumeCount:   disk.DiskInfo.DiskInfo.FreeVolumeCount,
+				}
+				diskCopy.DiskInfo = diskInfoCopy
+
+				available = append(available, &diskCopy)
+			}
+		}
+	}
+
+	return available
+}

weed/admin/topology/internal.go

@@ -64,7 +64,7 @@ func (at *ActiveTopology) assignTaskToDisk(task *taskState) {
 	}
 }
 
-// isDiskAvailable checks if a disk can accept new tasks
+// isDiskAvailable checks if a disk can accept new tasks (general availability)
 func (at *ActiveTopology) isDiskAvailable(disk *activeDisk, taskType TaskType) bool {
 	// Check if disk has too many pending and active tasks
 	activeLoad := len(disk.pendingTasks) + len(disk.assignedTasks)
@@ -72,9 +72,21 @@ func (at *ActiveTopology) isDiskAvailable(disk *activeDisk, taskType TaskType) b
 		return false
 	}
 
-	// Check for conflicting task types
+	// For general availability, only check disk capacity
+	// Volume-specific conflicts are checked in isDiskAvailableForVolume
+	return true
+}
+
+// isDiskAvailableForVolume checks if a disk can accept a new task for a specific volume
+func (at *ActiveTopology) isDiskAvailableForVolume(disk *activeDisk, taskType TaskType, volumeID uint32) bool {
+	// Check basic availability first
+	if !at.isDiskAvailable(disk, taskType) {
+		return false
+	}
+
+	// Check for volume-specific conflicts
 	for _, task := range disk.assignedTasks {
-		if at.areTaskTypesConflicting(task.TaskType, taskType) {
+		if at.areTasksConflicting(task, taskType, volumeID) {
 			return false
 		}
 	}
@@ -82,29 +94,28 @@ func (at *ActiveTopology) isDiskAvailable(disk *activeDisk, taskType TaskType) b
 	return true
 }
 
-// areTaskTypesConflicting checks if two task types conflict
-func (at *ActiveTopology) areTaskTypesConflicting(existing, new TaskType) bool {
-	// Define conflicting task types to prevent dangerous concurrent operations
-	// These conflicts prevent race conditions and data integrity issues
-	conflictMap := map[TaskType][]TaskType{
-		// Vacuum conflicts with balance and erasure coding (and ec_vacuum)
-		TaskType("vacuum"): {TaskType("balance"), TaskType("erasure_coding"), TaskType("ec_vacuum")},
-		
-		// Balance conflicts with vacuum and erasure coding operations
-		TaskType("balance"): {TaskType("vacuum"), TaskType("erasure_coding"), TaskType("ec_vacuum")},
-		
-		// Erasure coding conflicts with vacuum and balance operations
-		TaskType("erasure_coding"): {TaskType("vacuum"), TaskType("balance"), TaskType("ec_vacuum")},
-		
-		// EC vacuum conflicts with all other maintenance operations on same volume
-		TaskType("ec_vacuum"): {TaskType("vacuum"), TaskType("balance"), TaskType("erasure_coding")},
-		
-		// Replication generally should not conflict with read-only operations
-		// but should conflict with destructive operations
-		TaskType("replication"): {TaskType("vacuum"), TaskType("balance")},
+// areTasksConflicting checks if a new task conflicts with an existing task
+func (at *ActiveTopology) areTasksConflicting(existingTask *taskState, newTaskType TaskType, newVolumeID uint32) bool {
+	// PRIMARY RULE: Tasks on the same volume always conflict (prevents race conditions)
+	if existingTask.VolumeID == newVolumeID {
+		return true
+	}
+
+	// SECONDARY RULE: Some task types may have global conflicts (rare cases)
+	return at.areTaskTypesGloballyConflicting(existingTask.TaskType, newTaskType)
+}
+
+// areTaskTypesGloballyConflicting checks for rare global task type conflicts
+// These should be minimal - most conflicts should be volume-specific
+func (at *ActiveTopology) areTaskTypesGloballyConflicting(existing, new TaskType) bool {
+	// Define very limited global conflicts (cross-volume conflicts)
+	// Most conflicts should be volume-based, not global
+	globalConflictMap := map[TaskType][]TaskType{
+		// Example: Some hypothetical global resource conflicts could go here
+		// Currently empty - volume-based conflicts are sufficient
 	}
 
-	if conflicts, exists := conflictMap[existing]; exists {
+	if conflicts, exists := globalConflictMap[existing]; exists {
 		for _, conflictType := range conflicts {
 			if conflictType == new {
 				return true

weed/admin/topology/topology_management.go

@@ -89,6 +89,30 @@ func (at *ActiveTopology) GetAvailableDisks(taskType TaskType, excludeNodeID str
 	return available
 }
 
+// GetAvailableDisksForVolume returns disks that can accept a task for a specific volume
+// This method uses volume-aware conflict checking to prevent race conditions
+func (at *ActiveTopology) GetAvailableDisksForVolume(taskType TaskType, volumeID uint32, excludeNodeID string) []*DiskInfo {
+	at.mutex.RLock()
+	defer at.mutex.RUnlock()
+
+	var available []*DiskInfo
+
+	for _, disk := range at.disks {
+		if disk.NodeID == excludeNodeID {
+			continue // Skip excluded node
+		}
+
+		if at.isDiskAvailableForVolume(disk, taskType, volumeID) {
+			// Create a copy with current load count
+			diskCopy := *disk.DiskInfo
+			diskCopy.LoadCount = len(disk.pendingTasks) + len(disk.assignedTasks)
+			available = append(available, &diskCopy)
+		}
+	}
+
+	return available
+}
+
 // HasRecentTaskForVolume checks if a volume had a recent task (to avoid immediate re-detection)
 func (at *ActiveTopology) HasRecentTaskForVolume(volumeID uint32, taskType TaskType) bool {
 	at.mutex.RLock()