upstream-seaweedfs/weed/shell/command_volume_tier_move.go

package shell

import (
	"context"
	"errors"
	"flag"
	"fmt"
	"io"
	"sync"
	"time"

	"github.com/seaweedfs/seaweedfs/weed/placement"

	"github.com/seaweedfs/seaweedfs/weed/glog"
	"github.com/seaweedfs/seaweedfs/weed/operation/volume_move"
	"github.com/seaweedfs/seaweedfs/weed/pb"
	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
	"github.com/seaweedfs/seaweedfs/weed/storage/super_block"
	"github.com/seaweedfs/seaweedfs/weed/storage/types"
	"github.com/seaweedfs/seaweedfs/weed/util/wildcard"
	"github.com/seaweedfs/seaweedfs/weed/wdclient"

	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
	"github.com/seaweedfs/seaweedfs/weed/storage/volume_replica"
)

func init() {
	Commands = append(Commands, &commandVolumeTierMove{})
}

type volumeTierMoveJob struct {
	src pb.ServerAddress
	vid needle.VolumeId
	// replica already on target: skip the copy, just fulfill replication and clean up
	alreadyPlaced bool
}

type commandVolumeTierMove struct {
	activeServers sync.Map
	queues        map[pb.ServerAddress]chan volumeTierMoveJob
	//activeServers     map[pb.ServerAddress]struct{}
	//activeServersLock sync.Mutex
	//activeServersCond *sync.Cond
}

func (c *commandVolumeTierMove) Name() string {
	return "volume.tier.move"
}

func (c *commandVolumeTierMove) Help() string {
	return `change a volume from one disk type or data center to another

	volume.tier.move -fromDiskType=hdd -toDiskType=ssd [-collectionPattern=""] [-fullPercent=95] [-quietFor=1h] [-parallelLimit=4] [-toReplication=XYZ]
	volume.tier.move -fromDataCenter=dc1 -toDataCenter=dc2 [-collectionPattern=""] [-fullPercent=95] [-quietFor=1h]

	-fromDataCenter limits the volumes to move to those with a replica in that data center.
	-toDataCenter places the moved volumes in that data center.
	When fromDiskType and toDiskType are the same, both data center flags are required,
	and volumes are moved between data centers on the same disk type.

	The command ensures the target replication is fully achieved on the destination tier
	before deleting old replicas. This prevents data loss if a destination disk fails
	before replication repair completes.

	When -toReplication is specified, the moved volume is reconfigured with the new
	replication setting. Otherwise, the volume's existing replication is preserved.

	Note:
		-collectionPattern is a comma-separated list of collection names, with "*" and "?"
		wildcards, and regex patterns. Use "_default" to match only the default collection
		(volumes with no collection name). An empty pattern matches all collections.

`
}

func (c *commandVolumeTierMove) HasTag(CommandTag) bool {
	return false
}

func (c *commandVolumeTierMove) Do(args []string, commandEnv *CommandEnv, writer io.Writer) (err error) {

	tierCommand := flag.NewFlagSet(c.Name(), flag.ContinueOnError)
	collectionPattern := tierCommand.String("collectionPattern", "", "comma-separated collection names, with '*' and '?' wildcards; empty matches all")
	fullPercentage := tierCommand.Float64("fullPercent", 95, "the volume reaches the percentage of max volume size")
	quietPeriod := tierCommand.Duration("quietFor", 24*time.Hour, "select volumes without no writes for this period")
	source := tierCommand.String("fromDiskType", "", "the source disk type")
	target := tierCommand.String("toDiskType", "", "the target disk type")
	fromDataCenter := tierCommand.String("fromDataCenter", "", "only move volumes with a replica in this data center")
	toDataCenter := tierCommand.String("toDataCenter", "", "the target data center")
	parallelLimit := tierCommand.Int("parallelLimit", 0, "limit the number of parallel copying jobs")
	applyChange := tierCommand.Bool("apply", false, "actually apply the changes")
	// TODO: remove this alias
	applyChangeAlias := tierCommand.Bool("force", false, "actually apply the changes (alias for -apply)")
	ioBytePerSecond := tierCommand.Int64("ioBytePerSecond", 0, "limit the speed of move")
	replicationString := tierCommand.String("toReplication", "", "the new target replication setting")

	if err = tierCommand.Parse(args); err != nil {
		return nil
	}

	handleDeprecatedForceFlag(writer, tierCommand, applyChangeAlias, applyChange)
	infoAboutSimulationMode(writer, *applyChange, "-apply")

	if err = commandEnv.confirmIsLocked(args); err != nil {
		return
	}
	fromDiskType := types.ToDiskType(*source)
	toDiskType := types.ToDiskType(*target)

	if fromDiskType == toDiskType {
		if *fromDataCenter == "" || *toDataCenter == "" {
			return fmt.Errorf("source tier %s is the same as target tier %s; specify -fromDataCenter and -toDataCenter to move volumes between data centers", fromDiskType, toDiskType)
		}
		if *fromDataCenter == *toDataCenter {
			return fmt.Errorf("source data center %s is the same as target data center %s", *fromDataCenter, *toDataCenter)
		}
	}

	// collect topology information
	topologyInfo, volumeSizeLimitMb, err := collectTopologyInfo(commandEnv, 0)
	if err != nil {
		return err
	}

	// collect all volumes that should change
	volumeIds, err := collectVolumeIdsForTierChange(topologyInfo, volumeSizeLimitMb, fromDiskType, *fromDataCenter, *collectionPattern, *fullPercentage, *quietPeriod)
	if err != nil {
		return err
	}
	fmt.Printf("tier move volumes: %v\n", volumeIds)

	// Collect volume ID to collection name mapping for the sync operation
	volumeIdToCollection := collectVolumeIdToCollection(topologyInfo, volumeIds)

	volumeReplicas, allLocations := collectVolumeReplicaLocations(topologyInfo)
	allLocations = filterLocationsByDiskType(allLocations, toDiskType)
	if *toDataCenter != "" {
		allLocations = filterLocationsByDataCenter(allLocations, *toDataCenter)
	}
	keepDataNodesSorted(allLocations, toDiskType)
	if len(allLocations) == 0 {
		return fmt.Errorf("no volume server found with disk type %s%s", toDiskType.ReadableString(), dataCenterSuffix(*toDataCenter))
	}

	if len(allLocations) > 0 && *parallelLimit > 0 && *parallelLimit < len(allLocations) {
		allLocations = allLocations[:*parallelLimit]
	}

	wg := sync.WaitGroup{}
	bufferLen := len(allLocations)
	c.queues = make(map[pb.ServerAddress]chan volumeTierMoveJob)

	for _, dst := range allLocations {
		destServerAddress := pb.NewServerAddressFromDataNode(dst.dataNode)
		c.queues[destServerAddress] = make(chan volumeTierMoveJob, bufferLen)

		wg.Add(1)
		go func(dst location, jobs <-chan volumeTierMoveJob, applyChanges bool) {
			defer wg.Done()
			for job := range jobs {
				if job.alreadyPlaced {
					fmt.Fprintf(writer, "completing move of volume %d already on %s ...\n", job.vid, dst.dataNode.Id)
				} else {
					fmt.Fprintf(writer, "moving volume %d from %s to %s with disk type %s ...\n", job.vid, job.src, dst.dataNode.Id, toDiskType.ReadableString())
				}

				locations, found := commandEnv.MasterClient.GetLocationsClone(uint32(job.vid))
				if !found {
					fmt.Printf("volume %d not found", job.vid)
					continue
				}

				unlock := c.Lock(job.src)

				if applyChanges {
					if err := c.doMoveOneVolume(commandEnv, writer, job.vid, toDiskType, *toDataCenter, locations, job.src, dst, *ioBytePerSecond, replicationString, job.alreadyPlaced); err != nil {
						fmt.Fprintf(writer, "move volume %d %s => %s: %v\n", job.vid, job.src, dst.dataNode.Id, err)
					}
				}
				unlock()
			}
		}(dst, c.queues[destServerAddress], *applyChange)
	}

	for _, vid := range volumeIds {
		collection := volumeIdToCollection[vid]
		if err = c.doVolumeTierMove(commandEnv, writer, vid, collection, toDiskType, *toDataCenter, allLocations, volumeReplicas[uint32(vid)]); err != nil {
			fmt.Printf("tier move volume %d: %v\n", vid, err)
		}
		allLocations = rotateDataNodes(allLocations)
	}
	for key, _ := range c.queues {
		close(c.queues[key])
	}

	wg.Wait()

	return nil
}

func (c *commandVolumeTierMove) Lock(key pb.ServerAddress) func() {
	value, _ := c.activeServers.LoadOrStore(key, &sync.Mutex{})
	mtx := value.(*sync.Mutex)
	mtx.Lock()

	return func() { mtx.Unlock() }
}

func filterLocationsByDiskType(dataNodes []location, diskType types.DiskType) (ret []location) {
	for _, loc := range dataNodes {
		_, found := loc.dataNode.DiskInfos[string(diskType)]
		if found {
			ret = append(ret, loc)
		}
	}
	return
}

func filterLocationsByDataCenter(dataNodes []location, dataCenter string) (ret []location) {
	for _, loc := range dataNodes {
		if loc.dc == dataCenter {
			ret = append(ret, loc)
		}
	}
	return
}

func dataCenterSuffix(dataCenter string) string {
	if dataCenter == "" {
		return ""
	}
	return " in data center " + dataCenter
}

func rotateDataNodes(dataNodes []location) []location {
	if len(dataNodes) > 0 {
		return append(dataNodes[1:], dataNodes[0])
	} else {
		return dataNodes
	}
}

func isOneOf(server string, locations []wdclient.Location) bool {
	for _, loc := range locations {
		if server == loc.Url {
			return true
		}
	}
	return false
}

func (c *commandVolumeTierMove) doVolumeTierMove(commandEnv *CommandEnv, writer io.Writer, vid needle.VolumeId, collection string, toDiskType types.DiskType, toDataCenter string, allLocations []location, replicas []*VolumeReplica) (err error) {
	// find volume location
	locations, found := commandEnv.MasterClient.GetLocationsClone(uint32(vid))
	if !found {
		return fmt.Errorf("volume %d not found", vid)
	}

	// a replica already on the target tier (e.g. left by an interrupted earlier run)
	// anchors the move: skip the copy, only fulfill replication and clean up old replicas.
	// The anchor must match both the target disk type AND (when set) the target data
	// center, so a bare presence elsewhere never short-circuits a cross-DC move.
	// No replica sync is needed here: remote-tiered replicas share one cloud object,
	// so their content is byte-identical and there is no local divergence to reconcile.
	for _, r := range replicas {
		if types.ToDiskType(r.info.DiskType) != toDiskType || (toDataCenter != "" && r.location.dc != toDataCenter) {
			continue
		}
		anchorAddress := pb.NewServerAddressFromDataNode(r.location.dataNode)
		if queue, found := c.queues[anchorAddress]; found {
			fmt.Fprintf(writer, "volume %d is already on %s, will complete replication and cleanup\n", vid, r.location.dataNode.Id)
			queue <- volumeTierMoveJob{src: anchorAddress, vid: vid, alreadyPlaced: true}
			return nil
		}
	}

	// find one server with the most empty volume slots with target disk type
	hasFoundTarget := false
	fn := capacityByFreeVolumeCount(toDiskType)
	for _, dst := range allLocations {
		if fn(dst.dataNode) > 0 && !hasFoundTarget {
			// ask the volume server to replicate the volume
			if isOneOf(dst.dataNode.Id, locations) {
				continue
			}

			// Sync replicas and select the best one (with highest file count) for multi-replica volumes
			// This addresses data inconsistency risk in multi-replica volumes (issue #7797)
			// by syncing missing entries between replicas before moving
			sourceLoc, selectErr := volume_replica.SyncAndSelectBestReplica(
				commandEnv.option.GrpcDialOption, vid, collection, locations, dst.dataNode.Id, writer)
			if selectErr != nil {
				fmt.Fprintf(writer, "failed to sync and select source replica for volume %d: %v\n", vid, selectErr)
				continue
			}
			sourceVolumeServer := sourceLoc.ServerAddress()

			if sourceVolumeServer == "" {
				continue
			}
			hasFoundTarget = true

			// adjust volume count
			addVolumeCount(dst.dataNode.DiskInfos[string(toDiskType)], 1)

			destServerAddress := pb.NewServerAddressFromDataNode(dst.dataNode)
			c.queues[destServerAddress] <- volumeTierMoveJob{src: sourceVolumeServer, vid: vid}
		}
	}

	if !hasFoundTarget {
		fmt.Fprintf(writer, "can not find disk type %s%s for volume %d\n", toDiskType.ReadableString(), dataCenterSuffix(toDataCenter), vid)
	}

	return nil
}

func (c *commandVolumeTierMove) doMoveOneVolume(commandEnv *CommandEnv, writer io.Writer, vid needle.VolumeId, toDiskType types.DiskType, toDataCenter string, locations []wdclient.Location, sourceVolumeServer pb.ServerAddress, dst location, ioBytePerSecond int64, replicationString *string, alreadyPlaced bool) (err error) {

	if !commandEnv.isLocked() {
		return fmt.Errorf("lock is lost")
	}

	// mark all replicas as read only
	if err = markVolumeReplicasWritable(context.Background(), commandEnv.option.GrpcDialOption, vid, locations, false, false); err != nil {
		return fmt.Errorf("mark volume %d as readonly on %s: %v", vid, locations[0].Url, err)
	}
	newAddress := pb.NewServerAddressFromDataNode(dst.dataNode)

	// when already placed nothing is deleted yet, so failure paths restore every replica
	deletedSource := sourceVolumeServer
	if alreadyPlaced {
		deletedSource = ""
	} else if moveErr := LiveMoveVolume(context.Background(), commandEnv.option.GrpcDialOption, writer, vid, sourceVolumeServer, newAddress, 5*time.Second, toDiskType.ReadableString(), ioBytePerSecond); moveErr != nil {
		// A move that deliberately kept the source readonly (its delete may
		// have happened, leaving the target authoritative) must not be thawed
		// — reopening the replicas beside that copy would fork the volume.
		if !errors.Is(moveErr, volume_move.ErrSourceKeptReadonly) {
			// mark all replicas as writable
			if err = markVolumeReplicasWritable(context.Background(), commandEnv.option.GrpcDialOption, vid, locations, true, false); err != nil {
				glog.Errorf("mark volume %d as writable on %s: %v", vid, locations[0].Url, err)
			}
		}

		return fmt.Errorf("move volume %d %s => %s : %v", vid, locations[0].Url, dst.dataNode.Id, moveErr)
	}

	// If move is successful and replication is not empty, alter moved volume's replication setting
	if *replicationString != "" {
		if err = configureVolumeReplication(context.Background(), commandEnv.option.GrpcDialOption, vid, newAddress, *replicationString); err != nil {
			// LiveMoveVolume already deleted sourceVolumeServer; mark surviving
			// old replicas writable before aborting so the volume stays accessible.
			restoreSurvivingReplicasWritable(commandEnv, vid, locations, deletedSource)
			return fmt.Errorf("configure replication %s on volume %d at %s: %v", *replicationString, vid, newAddress, err)
		}
	}

	// Ensure the required number of replicas exist on the target tier BEFORE
	// deleting old replicas to avoid data-loss risk.
	// Use the explicit -toReplication if given, otherwise preserve the volume's
	// existing replication from the source tier.
	preserveServers, replicateErr := c.ensureReplicationFulfilled(commandEnv, writer, vid, toDiskType, toDataCenter, dst, *replicationString, ioBytePerSecond)
	if replicateErr != nil {
		// Replication not fully achieved — do NOT delete old replicas.
		restoreSurvivingReplicasWritable(commandEnv, vid, locations, deletedSource)
		return fmt.Errorf("volume %d moved to %s but failed to fulfill replication, old replicas preserved: %v", vid, dst.dataNode.Id, replicateErr)
	}

	// Mark preserved pre-existing target-tier replicas as writable.
	// They were marked read-only at the start of the move and would otherwise
	// stay read-only since we're keeping rather than deleting them.
	for _, loc := range locations {
		if preserveServers[loc.Url] {
			if markErr := markVolumeWritable(context.Background(), commandEnv.option.GrpcDialOption, vid, loc.ServerAddress(), true, false); markErr != nil {
				glog.Errorf("mark volume %d as writable on preserved replica %s: %v", vid, loc.Url, markErr)
			}
		}
	}

	// Remove old replicas that are NOT needed by the fulfilled replication.
	// Skip the move destination, the already-deleted source, and any pre-existing
	// target-tier replicas that were counted toward replication fulfillment.
	for _, loc := range locations {
		if loc.Url == dst.dataNode.Id || loc.ServerAddress() == sourceVolumeServer {
			continue
		}
		if preserveServers[loc.Url] {
			continue
		}
		// keepRemoteData=true: remote-tiered replicas share one cloud object, so
		// deleting a replica must not delete the object the survivors still point at.
		if err = deleteVolume(context.Background(), commandEnv.option.GrpcDialOption, vid, loc.ServerAddress(), false, true); err != nil {
			fmt.Fprintf(writer, "failed to delete volume %d on %s: %v\n", vid, loc.Url, err)
		}
	}
	return nil
}

// restoreSurvivingReplicasWritable marks old replicas writable after a failure,
// skipping the source that was already deleted by LiveMoveVolume.
func restoreSurvivingReplicasWritable(commandEnv *CommandEnv, vid needle.VolumeId, locations []wdclient.Location, deletedSource pb.ServerAddress) {
	for _, loc := range locations {
		if loc.ServerAddress() == deletedSource {
			continue
		}
		if markErr := markVolumeWritable(context.Background(), commandEnv.option.GrpcDialOption, vid, loc.ServerAddress(), true, false); markErr != nil {
			glog.Errorf("mark volume %d as writable on %s: %v", vid, loc.Url, markErr)
		}
	}
}

// ensureReplicationFulfilled creates additional replicas of the volume on the target tier
// to satisfy the requested replication placement. It re-collects topology after the initial
// move so it can see the newly placed volume and find suitable destinations for additional copies.
// It returns a set of server URLs (from the original locations) that host target-tier replicas
// counted toward fulfillment, so the caller can avoid deleting them during cleanup.
func (c *commandVolumeTierMove) ensureReplicationFulfilled(commandEnv *CommandEnv, writer io.Writer, vid needle.VolumeId, toDiskType types.DiskType, toDataCenter string, movedDst location, replicationString string, ioBytePerSecond int64) (preserveServers map[string]bool, err error) {
	preserveServers = make(map[string]bool)
	// keeps an anchored pre-existing replica writable on the early-return paths
	preserveServers[movedDst.dataNode.Id] = true
	sourceAddress := pb.NewServerAddressFromDataNode(movedDst.dataNode)

	// Wait briefly for the master to receive heartbeats reflecting the move,
	// then re-collect topology to get the current state.
	topologyInfo, _, err := collectTopologyInfo(commandEnv, 5*time.Second)
	if err != nil {
		return nil, fmt.Errorf("collect topology: %v", err)
	}

	volumeReplicas, allLocations := collectVolumeReplicaLocations(topologyInfo)
	allLocations = filterLocationsByDiskType(allLocations, toDiskType)
	if toDataCenter != "" {
		allLocations = filterLocationsByDataCenter(allLocations, toDataCenter)
	}
	keepDataNodesSorted(allLocations, toDiskType)

	existingReplicas := volumeReplicas[uint32(vid)]
	if len(existingReplicas) == 0 {
		return nil, fmt.Errorf("volume %d not found in topology after move", vid)
	}

	// Build a set of all data nodes that already host this volume (any disk type)
	// so we don't try to VolumeCopy to a server that already has it.
	nodesWithVolume := make(map[string]bool)
	for _, r := range existingReplicas {
		nodesWithVolume[r.location.dataNode.Id] = true
	}

	// Determine the target replication: use explicit -toReplication if given,
	// otherwise read the volume's existing replication setting.
	var replicaPlacement *super_block.ReplicaPlacement
	if replicationString != "" {
		replicaPlacement, err = super_block.NewReplicaPlacementFromString(replicationString)
		if err != nil {
			return nil, fmt.Errorf("parse replication %s: %v", replicationString, err)
		}
	} else {
		replicaPlacement, err = super_block.NewReplicaPlacementFromByte(byte(existingReplicas[0].info.ReplicaPlacement))
		if err != nil {
			return nil, fmt.Errorf("parse existing replication for volume %d: %v", vid, err)
		}
	}

	requiredCopies := replicaPlacement.GetCopyCount()
	if requiredCopies <= 1 {
		// No additional replicas needed (e.g., replication "000")
		return preserveServers, nil
	}

	// Filter to only replicas on the target disk type and data center (the newly moved one).
	var targetTierReplicas []*VolumeReplica
	for _, r := range existingReplicas {
		if types.ToDiskType(r.info.DiskType) == toDiskType && (toDataCenter == "" || r.location.dc == toDataCenter) {
			targetTierReplicas = append(targetTierReplicas, r)
			// Track pre-existing target-tier replicas so the caller won't delete them.
			preserveServers[r.location.dataNode.Id] = true
		}
	}
	if len(targetTierReplicas) == 0 {
		return nil, fmt.Errorf("volume %d not found on target tier %s%s in topology after move", vid, toDiskType, dataCenterSuffix(toDataCenter))
	}

	// Ensure all existing target-tier replicas have the correct replication metadata.
	// The primary moved replica is already configured in doMoveOneVolume, but there may
	// be pre-existing replicas on the target tier that need updating.
	if replicationString != "" {
		for _, r := range targetTierReplicas {
			addr := pb.NewServerAddressFromDataNode(r.location.dataNode)
			if configErr := configureVolumeReplication(context.Background(), commandEnv.option.GrpcDialOption, vid, addr, replicationString); configErr != nil {
				return nil, fmt.Errorf("volume %d: failed to configure replication on existing replica %s: %v", vid, r.location.dataNode.Id, configErr)
			}
		}
	}

	additionalCopiesNeeded := requiredCopies - len(targetTierReplicas)
	if additionalCopiesNeeded <= 0 {
		return preserveServers, nil
	}

	fmt.Fprintf(writer, "volume %d: creating %d additional replica(s) for replication %s\n", vid, additionalCopiesNeeded, replicaPlacement)

	// One picker decides where copies go, so this command spreads and stays near
	// the source the same way every other mover does. Constraints it cannot model
	// -- replica placement, and a node already holding the volume -- stay here.
	topo := topologyFromLocations(allLocations)
	// The picker answers with a node; replica placement is judged on where that
	// node sits, so keep the mapping back to its rack and data center.
	placeOf := make(map[string]location, len(allLocations))
	for _, l := range allLocations {
		placeOf[l.dataNode.Id] = l
	}
	taken := make(map[string]bool)
	copiesMade := 0
	for copiesMade < additionalCopiesNeeded {
		dst := placement.PickTarget(topo, placement.PlacementPreference{
			Source:   sourceAddress.String(),
			DiskType: toDiskType,
			Exclude:  taken,
			Accept: func(dn *master_pb.DataNodeInfo, dc, rack string) bool {
				if nodesWithVolume[dn.Id] {
					return false
				}
				return satisfyReplicaPlacement(replicaPlacement, targetTierReplicas, newLocation(dc, rack, dn))
			},
		})
		if dst == nil {
			break
		}
		taken[dst.Id] = true
		candidateDst := placeOf[dst.Id]
		candidateAddress := pb.NewServerAddressFromDataNode(dst)

		if copyErr := replicateVolumeToServer(context.Background(), commandEnv.option.GrpcDialOption, writer, vid, sourceAddress, candidateAddress, toDiskType.ReadableString(), ioBytePerSecond); copyErr != nil {
			return nil, fmt.Errorf("replicate volume %d to %s: %v", vid, candidateDst.dataNode.Id, copyErr)
		}

		// Configure replication on the new replica if an explicit -toReplication was given.
		// Without it, VolumeCopy already preserves the source's replication from the super block.
		if replicationString != "" {
			if configErr := configureVolumeReplication(context.Background(), commandEnv.option.GrpcDialOption, vid, candidateAddress, replicationString); configErr != nil {
				return nil, fmt.Errorf("volume %d: failed to configure replication on %s: %v", vid, candidateDst.dataNode.Id, configErr)
			}
		}

		// Track the new replica for placement decisions
		targetTierReplicas = append(targetTierReplicas, &VolumeReplica{
			location: &candidateDst,
			info:     targetTierReplicas[0].info,
		})
		// PickTarget already spent the slot in topo, which shares these DataNodeInfo
		// pointers with allLocations, so counting it again here would double it.
		copiesMade++
	}

	if copiesMade < additionalCopiesNeeded {
		return nil, fmt.Errorf("could only create %d of %d additional replicas for volume %d (replication %s): not enough eligible destinations", copiesMade, additionalCopiesNeeded, vid, replicaPlacement)
	}

	fmt.Fprintf(writer, "volume %d: replication %s fulfilled with %d total copies\n", vid, replicaPlacement, requiredCopies)
	return preserveServers, nil
}

func collectVolumeIdsForTierChange(topologyInfo *master_pb.TopologyInfo, volumeSizeLimitMb uint64, sourceTier types.DiskType, sourceDataCenter string, collectionPattern string, fullPercentage float64, quietPeriod time.Duration) (vids []needle.VolumeId, err error) {

	collectionMatcher, err := wildcard.CompileCollectionMatcher(collectionPattern)
	if err != nil {
		return nil, err
	}

	quietSeconds := int64(quietPeriod / time.Second)
	nowUnixSeconds := time.Now().Unix()

	fmt.Printf("collect %s volumes quiet for: %d seconds\n", sourceTier, quietSeconds)

	vidMap := make(map[uint32]bool)
	eachDataNode(topologyInfo, func(dc DataCenterId, rack RackId, dn *master_pb.DataNodeInfo) {
		if sourceDataCenter != "" && string(dc) != sourceDataCenter {
			return
		}
		for _, diskInfo := range dn.DiskInfos {
			for _, v := range diskInfo.VolumeInfos {
				if !collectionMatcher.Matches(v.Collection) {
					continue
				}

				if v.ModifiedAtSecond+quietSeconds < nowUnixSeconds && types.ToDiskType(v.DiskType) == sourceTier {
					if float64(v.Size) > fullPercentage/100*float64(volumeSizeLimitMb)*1024*1024 {
						vidMap[v.Id] = true
					}
				}
			}
		}
	})

	// Check if an error occurred during iteration and return early
	if err != nil {
		return
	}

	for vid := range vidMap {
		vids = append(vids, needle.VolumeId(vid))
	}

	return
}

// topologyFromLocations rebuilds a topology snapshot from the locations a
// command already collected, so placement sees exactly the candidate set the
// command would have iterated.
func topologyFromLocations(locations []location) *master_pb.TopologyInfo {
	dcs := make(map[string]map[string][]*master_pb.DataNodeInfo)
	var dcOrder []string
	rackOrder := make(map[string][]string)
	for _, l := range locations {
		if _, ok := dcs[l.dc]; !ok {
			dcs[l.dc] = make(map[string][]*master_pb.DataNodeInfo)
			dcOrder = append(dcOrder, l.dc)
		}
		if _, ok := dcs[l.dc][l.rack]; !ok {
			rackOrder[l.dc] = append(rackOrder[l.dc], l.rack)
		}
		dcs[l.dc][l.rack] = append(dcs[l.dc][l.rack], l.dataNode)
	}
	topo := &master_pb.TopologyInfo{}
	for _, dc := range dcOrder {
		dcInfo := &master_pb.DataCenterInfo{Id: dc}
		for _, rack := range rackOrder[dc] {
			dcInfo.RackInfos = append(dcInfo.RackInfos, &master_pb.RackInfo{Id: rack, DataNodeInfos: dcs[dc][rack]})
		}
		topo.DataCenterInfos = append(topo.DataCenterInfos, dcInfo)
	}
	return topo
}