crawler: Missing folder heal check per set (#10876)

cmd/data-crawler.go

@@ -148,6 +148,7 @@ type folderScanner struct {
 
 	newFolders      []cachedFolder
 	existingFolders []cachedFolder
+	disks           []StorageAPI
 }
 
 // crawlDataFolder will crawl the basepath+cache.Info.Name and return an updated cache.
@@ -176,7 +177,6 @@ func crawlDataFolder(ctx context.Context, basePath string, cache dataUsageCache,
 		logger.LogIf(ctx, err)
 		delayMult = dataCrawlSleepDefMult
 	}
-
 	s := folderScanner{
 		root:                basePath,
 		getSize:             getSize,
@@ -190,6 +190,18 @@ func crawlDataFolder(ctx context.Context, basePath string, cache dataUsageCache,
 		healObjectSelect:    0,
 	}
 
+	// Add disks for set healing.
+	if len(cache.Disks) > 0 {
+		objAPI, ok := newObjectLayerFn().(*erasureServerSets)
+		if ok {
+			s.disks = objAPI.GetDisksID(cache.Disks...)
+			if len(s.disks) != len(cache.Disks) {
+				logger.Info(logPrefix+"Missing disks, want %d, found %d. Cannot heal."+logSuffix, len(cache.Disks), len(s.disks))
+				s.disks = s.disks[:0]
+			}
+		}
+	}
+
 	// Enable healing in XL mode.
 	if globalIsErasure {
 		// Include a clean folder one in n cycles.
@@ -459,8 +471,8 @@ func (f *folderScanner) scanQueuedLevels(ctx context.Context, folders []cachedFo
 			continue
 		}
 
-		objAPI := newObjectLayerFn()
+		objAPI, ok := newObjectLayerFn().(*erasureServerSets)
-		if objAPI == nil {
+		if !ok || len(f.disks) == 0 {
 			continue
 		}
 
@@ -480,6 +492,13 @@ func (f *folderScanner) scanQueuedLevels(ctx context.Context, folders []cachedFo
 		// We therefore perform a heal check.
 		// If that doesn't bring it back we remove the folder and assume it was deleted.
 		// This means that the next run will not look for it.
+		// How to resolve results.
+		resolver := metadataResolutionParams{
+			dirQuorum: getReadQuorum(len(f.disks)),
+			objQuorum: getReadQuorum(len(f.disks)),
+			bucket:    "",
+		}
+
 		for k := range existing {
 			bucket, prefix := path2BucketObject(k)
 			if f.dataUsageCrawlDebug {
@@ -488,30 +507,121 @@ func (f *folderScanner) scanQueuedLevels(ctx context.Context, folders []cachedFo
 
 			// Dynamic time delay.
 			t := UTCNow()
+			resolver.bucket = bucket
 
-			err = objAPI.HealObjects(ctx, bucket, prefix, madmin.HealOpts{Recursive: true, Remove: healDeleteDangling},
+			foundObjs := false
-				func(bucket, object, versionID string) error {
+			dangling := true
-					// Wait for each heal as per crawler frequency.
+			ctx, cancel := context.WithCancel(ctx)
+			err := listPathRaw(ctx, listPathRawOptions{
+				disks:          f.disks,
+				bucket:         bucket,
+				path:           prefix,
+				recursive:      true,
+				reportNotFound: true,
+				minDisks:       len(f.disks), // We want full consistency.
+				// Weird, maybe transient error.
+				agreed: func(entry metaCacheEntry) {
+					if f.dataUsageCrawlDebug {
+						logger.Info(color.Green("healObjects:")+" got agreement: %v", entry.name)
+					}
+					if entry.isObject() {
+						dangling = false
+					}
+				},
+				// Some disks have data for this.
+				partial: func(entries metaCacheEntries, nAgreed int, errs []error) {
+					if f.dataUsageCrawlDebug {
+						logger.Info(color.Green("healObjects:")+" got partial, %d agreed, errs: %v", nAgreed, errs)
+					}
+					// Sleep and reset.
 					sleepDuration(time.Since(t), f.dataUsageCrawlMult)
+					t = UTCNow()
+					entry, ok := entries.resolve(&resolver)
+					if !ok {
+						for _, err := range errs {
+							if err != nil {
+								// Not all disks are ready, do nothing for now.
+								dangling = false
+								return
+							}
+						}
 
-					defer func() {
+						// If no errors, queue it for healing.
+						entry, _ = entries.firstFound()
+					}
+
+					if f.dataUsageCrawlDebug {
+						logger.Info(color.Green("healObjects:")+" resolved to: %v, dir: %v", entry.name, entry.isDir())
+					}
+					if entry.isDir() {
+						return
+					}
+					dangling = false
+					// We got an entry which we should be able to heal.
+					fiv, err := entry.fileInfoVersions(bucket)
+					if err != nil {
+						err := bgSeq.queueHealTask(healSource{
+							bucket:    bucket,
+							object:    entry.name,
+							versionID: "",
+						}, madmin.HealItemObject)
+						logger.LogIf(ctx, err)
+						foundObjs = foundObjs || err == nil
+						return
+					}
+					for _, ver := range fiv.Versions {
+						// Sleep and reset.
+						sleepDuration(time.Since(t), f.dataUsageCrawlMult)
 						t = UTCNow()
-					}()
+						err := bgSeq.queueHealTask(healSource{
-					return bgSeq.queueHealTask(healSource{
+							bucket:    bucket,
-						bucket:    bucket,
+							object:    fiv.Name,
-						object:    object,
+							versionID: ver.VersionID,
-						versionID: versionID,
+						}, madmin.HealItemObject)
-					}, madmin.HealItemObject)
+						logger.LogIf(ctx, err)
-				})
+						foundObjs = foundObjs || err == nil
+					}
+				},
+				// Too many disks failed.
+				finished: func(errs []error) {
+					if f.dataUsageCrawlDebug {
+						logger.Info(color.Green("healObjects:")+" too many errors: %v", errs)
+					}
+					dangling = false
+					cancel()
+				},
+			})
+
+			if f.dataUsageCrawlDebug && err != nil && err != errFileNotFound {
+				logger.Info(color.Green("healObjects:")+" checking returned value %v (%T)", err, err)
+			}
+
+			// If we found one or more disks with this folder, delete it.
+			if err == nil && dangling {
+				if f.dataUsageCrawlDebug {
+					logger.Info(color.Green("healObjects:")+" deleting dangling directory %s", prefix)
+				}
+				// If we have quorum, found directories, but no objects, issue heal to delete the dangling.
+				objAPI.HealObjects(ctx, bucket, prefix, madmin.HealOpts{Recursive: true, Remove: true},
+					func(bucket, object, versionID string) error {
+						// Wait for each heal as per crawler frequency.
+						sleepDuration(time.Since(t), f.dataUsageCrawlMult)
+
+						defer func() {
+							t = UTCNow()
+						}()
+						return bgSeq.queueHealTask(healSource{
+							bucket:    bucket,
+							object:    object,
+							versionID: versionID,
+						}, madmin.HealItemObject)
+					})
+			}
 
 			sleepDuration(time.Since(t), f.dataUsageCrawlMult)
 
-			if f.dataUsageCrawlDebug && err != nil {
-				logger.Info(color.Green("healObjects:")+" checking returned value %v", err)
-			}
-
 			// Add unless healing returned an error.
-			if err == nil {
+			if foundObjs {
 				this := cachedFolder{name: k, parent: &thisHash, objectHealProbDiv: folder.objectHealProbDiv}
 				cache.addChild(hashPath(k))
 				if final {

cmd/data-usage-cache.go

@@ -56,6 +56,7 @@ type dataUsageEntry struct {
 // dataUsageCache contains a cache of data usage entries.
 type dataUsageCache struct {
 	Info  dataUsageCacheInfo
+	Disks []string
 	Cache map[string]dataUsageEntry
 }
 

cmd/data-usage-cache_gen.go

@@ -30,35 +30,54 @@ func (z *dataUsageCache) DecodeMsg(dc *msgp.Reader) (err error) {
 				err = msgp.WrapError(err, "Info")
 				return
 			}
-		case "Cache":
+		case "Disks":
 			var zb0002 uint32
-			zb0002, err = dc.ReadMapHeader()
+			zb0002, err = dc.ReadArrayHeader()
+			if err != nil {
+				err = msgp.WrapError(err, "Disks")
+				return
+			}
+			if cap(z.Disks) >= int(zb0002) {
+				z.Disks = (z.Disks)[:zb0002]
+			} else {
+				z.Disks = make([]string, zb0002)
+			}
+			for za0001 := range z.Disks {
+				z.Disks[za0001], err = dc.ReadString()
+				if err != nil {
+					err = msgp.WrapError(err, "Disks", za0001)
+					return
+				}
+			}
+		case "Cache":
+			var zb0003 uint32
+			zb0003, err = dc.ReadMapHeader()
 			if err != nil {
 				err = msgp.WrapError(err, "Cache")
 				return
 			}
 			if z.Cache == nil {
-				z.Cache = make(map[string]dataUsageEntry, zb0002)
+				z.Cache = make(map[string]dataUsageEntry, zb0003)
 			} else if len(z.Cache) > 0 {
 				for key := range z.Cache {
 					delete(z.Cache, key)
 				}
 			}
-			for zb0002 > 0 {
+			for zb0003 > 0 {
-				zb0002--
+				zb0003--
-				var za0001 string
+				var za0002 string
-				var za0002 dataUsageEntry
+				var za0003 dataUsageEntry
-				za0001, err = dc.ReadString()
+				za0002, err = dc.ReadString()
 				if err != nil {
 					err = msgp.WrapError(err, "Cache")
 					return
 				}
-				err = za0002.DecodeMsg(dc)
+				err = za0003.DecodeMsg(dc)
 				if err != nil {
-					err = msgp.WrapError(err, "Cache", za0001)
+					err = msgp.WrapError(err, "Cache", za0002)
 					return
 				}
-				z.Cache[za0001] = za0002
+				z.Cache[za0002] = za0003
 			}
 		default:
 			err = dc.Skip()
@@ -73,9 +92,9 @@ func (z *dataUsageCache) DecodeMsg(dc *msgp.Reader) (err error) {
 
 // EncodeMsg implements msgp.Encodable
 func (z *dataUsageCache) EncodeMsg(en *msgp.Writer) (err error) {
-	// map header, size 2
+	// map header, size 3
 	// write "Info"
-	err = en.Append(0x82, 0xa4, 0x49, 0x6e, 0x66, 0x6f)
+	err = en.Append(0x83, 0xa4, 0x49, 0x6e, 0x66, 0x6f)
 	if err != nil {
 		return
 	}
@@ -84,6 +103,23 @@ func (z *dataUsageCache) EncodeMsg(en *msgp.Writer) (err error) {
 		err = msgp.WrapError(err, "Info")
 		return
 	}
+	// write "Disks"
+	err = en.Append(0xa5, 0x44, 0x69, 0x73, 0x6b, 0x73)
+	if err != nil {
+		return
+	}
+	err = en.WriteArrayHeader(uint32(len(z.Disks)))
+	if err != nil {
+		err = msgp.WrapError(err, "Disks")
+		return
+	}
+	for za0001 := range z.Disks {
+		err = en.WriteString(z.Disks[za0001])
+		if err != nil {
+			err = msgp.WrapError(err, "Disks", za0001)
+			return
+		}
+	}
 	// write "Cache"
 	err = en.Append(0xa5, 0x43, 0x61, 0x63, 0x68, 0x65)
 	if err != nil {
@@ -94,15 +130,15 @@ func (z *dataUsageCache) EncodeMsg(en *msgp.Writer) (err error) {
 		err = msgp.WrapError(err, "Cache")
 		return
 	}
-	for za0001, za0002 := range z.Cache {
+	for za0002, za0003 := range z.Cache {
-		err = en.WriteString(za0001)
+		err = en.WriteString(za0002)
 		if err != nil {
 			err = msgp.WrapError(err, "Cache")
 			return
 		}
-		err = za0002.EncodeMsg(en)
+		err = za0003.EncodeMsg(en)
 		if err != nil {
-			err = msgp.WrapError(err, "Cache", za0001)
+			err = msgp.WrapError(err, "Cache", za0002)
 			return
 		}
 	}
@@ -112,22 +148,28 @@ func (z *dataUsageCache) EncodeMsg(en *msgp.Writer) (err error) {
 // MarshalMsg implements msgp.Marshaler
 func (z *dataUsageCache) MarshalMsg(b []byte) (o []byte, err error) {
 	o = msgp.Require(b, z.Msgsize())
-	// map header, size 2
+	// map header, size 3
 	// string "Info"
-	o = append(o, 0x82, 0xa4, 0x49, 0x6e, 0x66, 0x6f)
+	o = append(o, 0x83, 0xa4, 0x49, 0x6e, 0x66, 0x6f)
 	o, err = z.Info.MarshalMsg(o)
 	if err != nil {
 		err = msgp.WrapError(err, "Info")
 		return
 	}
+	// string "Disks"
+	o = append(o, 0xa5, 0x44, 0x69, 0x73, 0x6b, 0x73)
+	o = msgp.AppendArrayHeader(o, uint32(len(z.Disks)))
+	for za0001 := range z.Disks {
+		o = msgp.AppendString(o, z.Disks[za0001])
+	}
 	// string "Cache"
 	o = append(o, 0xa5, 0x43, 0x61, 0x63, 0x68, 0x65)
 	o = msgp.AppendMapHeader(o, uint32(len(z.Cache)))
-	for za0001, za0002 := range z.Cache {
+	for za0002, za0003 := range z.Cache {
-		o = msgp.AppendString(o, za0001)
+		o = msgp.AppendString(o, za0002)
-		o, err = za0002.MarshalMsg(o)
+		o, err = za0003.MarshalMsg(o)
 		if err != nil {
-			err = msgp.WrapError(err, "Cache", za0001)
+			err = msgp.WrapError(err, "Cache", za0002)
 			return
 		}
 	}
@@ -158,35 +200,54 @@ func (z *dataUsageCache) UnmarshalMsg(bts []byte) (o []byte, err error) {
 				err = msgp.WrapError(err, "Info")
 				return
 			}
-		case "Cache":
+		case "Disks":
 			var zb0002 uint32
-			zb0002, bts, err = msgp.ReadMapHeaderBytes(bts)
+			zb0002, bts, err = msgp.ReadArrayHeaderBytes(bts)
+			if err != nil {
+				err = msgp.WrapError(err, "Disks")
+				return
+			}
+			if cap(z.Disks) >= int(zb0002) {
+				z.Disks = (z.Disks)[:zb0002]
+			} else {
+				z.Disks = make([]string, zb0002)
+			}
+			for za0001 := range z.Disks {
+				z.Disks[za0001], bts, err = msgp.ReadStringBytes(bts)
+				if err != nil {
+					err = msgp.WrapError(err, "Disks", za0001)
+					return
+				}
+			}
+		case "Cache":
+			var zb0003 uint32
+			zb0003, bts, err = msgp.ReadMapHeaderBytes(bts)
 			if err != nil {
 				err = msgp.WrapError(err, "Cache")
 				return
 			}
 			if z.Cache == nil {
-				z.Cache = make(map[string]dataUsageEntry, zb0002)
+				z.Cache = make(map[string]dataUsageEntry, zb0003)
 			} else if len(z.Cache) > 0 {
 				for key := range z.Cache {
 					delete(z.Cache, key)
 				}
 			}
-			for zb0002 > 0 {
+			for zb0003 > 0 {
-				var za0001 string
+				var za0002 string
-				var za0002 dataUsageEntry
+				var za0003 dataUsageEntry
-				zb0002--
+				zb0003--
-				za0001, bts, err = msgp.ReadStringBytes(bts)
+				za0002, bts, err = msgp.ReadStringBytes(bts)
 				if err != nil {
 					err = msgp.WrapError(err, "Cache")
 					return
 				}
-				bts, err = za0002.UnmarshalMsg(bts)
+				bts, err = za0003.UnmarshalMsg(bts)
 				if err != nil {
-					err = msgp.WrapError(err, "Cache", za0001)
+					err = msgp.WrapError(err, "Cache", za0002)
 					return
 				}
-				z.Cache[za0001] = za0002
+				z.Cache[za0002] = za0003
 			}
 		default:
 			bts, err = msgp.Skip(bts)
@@ -202,11 +263,15 @@ func (z *dataUsageCache) UnmarshalMsg(bts []byte) (o []byte, err error) {
 
 // Msgsize returns an upper bound estimate of the number of bytes occupied by the serialized message
 func (z *dataUsageCache) Msgsize() (s int) {
-	s = 1 + 5 + z.Info.Msgsize() + 6 + msgp.MapHeaderSize
+	s = 1 + 5 + z.Info.Msgsize() + 6 + msgp.ArrayHeaderSize
+	for za0001 := range z.Disks {
+		s += msgp.StringPrefixSize + len(z.Disks[za0001])
+	}
+	s += 6 + msgp.MapHeaderSize
 	if z.Cache != nil {
-		for za0001, za0002 := range z.Cache {
+		for za0002, za0003 := range z.Cache {
-			_ = za0002
+			_ = za0003
-			s += msgp.StringPrefixSize + len(za0001) + za0002.Msgsize()
+			s += msgp.StringPrefixSize + len(za0002) + za0003.Msgsize()
 		}
 	}
 	return

cmd/erasure-server-sets.go

@@ -92,6 +92,26 @@ func (z *erasureServerSets) NewNSLock(bucket string, objects ...string) RWLocker
 	return z.serverSets[0].NewNSLock(bucket, objects...)
 }
 
+// GetDisksID will return disks by their ID.
+func (z *erasureServerSets) GetDisksID(ids ...string) []StorageAPI {
+	idMap := make(map[string]struct{})
+	for _, id := range ids {
+		idMap[id] = struct{}{}
+	}
+	res := make([]StorageAPI, 0, len(idMap))
+	for _, ss := range z.serverSets {
+		for _, disks := range ss.erasureDisks {
+			for _, disk := range disks {
+				id, _ := disk.GetDiskID()
+				if _, ok := idMap[id]; ok {
+					res = append(res, disk)
+				}
+			}
+		}
+	}
+	return res
+}
+
 func (z *erasureServerSets) GetAllLockers() []dsync.NetLocker {
 	return z.serverSets[0].GetAllLockers()
 }

cmd/erasure.go

@@ -252,6 +252,14 @@ func (er erasureObjects) crawlAndGetDataUsage(ctx context.Context, buckets []Buc
 		return nil
 	}
 
+	// Collect disks for healing.
+	allDisks := er.getDisks()
+	allDiskIDs := make([]string, len(allDisks))
+	for i, disk := range allDisks {
+		id, _ := disk.GetDiskID()
+		allDiskIDs[i] = id
+	}
+
 	// Load bucket totals
 	oldCache := dataUsageCache{}
 	if err := oldCache.load(ctx, er, dataUsageCacheName); err != nil {
@@ -351,6 +359,7 @@ func (er erasureObjects) crawlAndGetDataUsage(ctx context.Context, buckets []Buc
 					cache.Info.Name = bucket.Name
 				}
 				cache.Info.BloomFilter = bloom
+				cache.Disks = allDiskIDs
 				if cache.Info.Name != bucket.Name {
 					logger.LogIf(ctx, fmt.Errorf("cache name mismatch: %s != %s", cache.Info.Name, bucket.Name))
 					cache.Info = dataUsageCacheInfo{

cmd/metacache-entries.go

@@ -246,6 +246,19 @@ func (m metaCacheEntries) resolve(r *metadataResolutionParams) (selected *metaCa
 	return selected, selected != nil
 }
 
+// firstFound returns the first found and the number of set entries.
+func (m metaCacheEntries) firstFound() (first *metaCacheEntry, n int) {
+	for _, entry := range m {
+		if entry.name != "" {
+			n++
+			if first == nil {
+				first = &entry
+			}
+		}
+	}
+	return first, n
+}
+
 // names will return all names in order.
 // Since this allocates it should not be used in critical functions.
 func (m metaCacheEntries) names() []string {

cmd/metacache-set.go

@@ -627,29 +627,6 @@ func (er *erasureObjects) listPath(ctx context.Context, o listPathOptions) (entr
 		disks = disks[:askDisks]
 	}
 
-	var readers = make([]*metacacheReader, askDisks)
-	for i := range disks {
-		r, w := io.Pipe()
-		d := disks[i]
-		readers[i], err = newMetacacheReader(r)
-		if err != nil {
-			cancel()
-			return entries, err
-		}
-		// Send request to each disk.
-		go func() {
-			err := d.WalkDir(ctx, WalkDirOptions{
-				Bucket:       o.Bucket,
-				BaseDir:      o.BaseDir,
-				Recursive:    o.Recursive || o.Separator != SlashSeparator,
-				FilterPrefix: o.FilterPrefix}, w)
-			w.CloseWithError(err)
-			if err != io.EOF {
-				logger.LogIf(ctx, err)
-			}
-		}()
-	}
-
 	// Create output for our results.
 	cacheCh := make(chan metaCacheEntry, metacacheBlockSize)
 
@@ -746,92 +723,38 @@ func (er *erasureObjects) listPath(ctx context.Context, o listPathOptions) (entr
 			bucket:    o.Bucket,
 		}
 
-		topEntries := make(metaCacheEntries, len(readers))
+		err := listPathRaw(ctx, listPathRawOptions{
-		for {
+			disks:        disks,
-			// Get the top entry from each
+			bucket:       o.Bucket,
-			var current metaCacheEntry
+			path:         o.BaseDir,
-			var atEOF, agree int
+			recursive:    o.Recursive,
-			for i, r := range readers {
+			filterPrefix: o.FilterPrefix,
-				topEntries[i].name = ""
+			minDisks:     askDisks - 1,
-				entry, err := r.peek()
+			agreed: func(entry metaCacheEntry) {
-				switch err {
+				cacheCh <- entry
-				case io.EOF:
+				filterCh <- entry
-					atEOF++
+			},
-					continue
+			partial: func(entries metaCacheEntries, nAgreed int, errs []error) {
-				case nil:
+				// Results Disagree :-(
-				default:
+				entry, ok := entries.resolve(&resolver)
-					closeChannels()
+				if ok {
-					metaMu.Lock()
+					cacheCh <- *entry
-					meta.status = scanStateError
+					filterCh <- *entry
-					meta.error = err.Error()
-					metaMu.Unlock()
-					return
 				}
-				// If no current, add it.
+			},
-				if current.name == "" {
+		})
-					topEntries[i] = entry
-					current = entry
-					agree++
-					continue
-				}
-				// If exact match, we agree.
-				if current.matches(&entry, o.Bucket) {
-					topEntries[i] = entry
-					agree++
-					continue
-				}
-				// If only the name matches we didn't agree, but add it for resolution.
-				if entry.name == current.name {
-					topEntries[i] = entry
-					continue
-				}
-				// We got different entries
-				if entry.name > current.name {
-					continue
-				}
-				// We got a new, better current.
-				// Clear existing entries.
-				for i := range topEntries[:i] {
-					topEntries[i] = metaCacheEntry{}
-				}
-				agree = 1
-				current = entry
-				topEntries[i] = entry
-			}
-			// Break if all at EOF.
-			if atEOF == len(readers) {
-				break
-			}
-			if agree == len(readers) {
-				// Everybody agreed
-				for _, r := range readers {
-					r.skip(1)
-				}
-				cacheCh <- topEntries[0]
-				filterCh <- topEntries[0]
-				continue
-			}
 
-			// Results Disagree :-(
-			entry, ok := topEntries.resolve(&resolver)
-			if ok {
-				cacheCh <- *entry
-				filterCh <- *entry
-			}
-			// Skip the inputs we used.
-			for i, r := range readers {
-				if topEntries[i].name != "" {
-					r.skip(1)
-				}
-			}
-		}
-
-		// Save success
 		metaMu.Lock()
+		if err != nil {
+			meta.status = scanStateError
+			meta.error = err.Error()
+		}
+		// Save success
 		if meta.error == "" {
 			meta.status = scanStateSuccess
 			meta.endedCycle = intDataUpdateTracker.current()
 		}
+
 		meta, _ = o.updateMetacacheListing(meta, rpc)
 		metaMu.Unlock()
 
@@ -847,3 +770,184 @@ func (er *erasureObjects) listPath(ctx context.Context, o listPathOptions) (entr
 
 	return filteredResults()
 }
+
+type listPathRawOptions struct {
+	disks        []StorageAPI
+	bucket, path string
+	recursive    bool
+	filterPrefix string
+	// Minimum number of good disks to continue.
+	// An error will be returned if this many disks returned an error.
+	minDisks       int
+	reportNotFound bool
+
+	// Callbacks with results:
+	// If set to nil, it will not be called.
+
+	// agreed is called if all disks agreed.
+	agreed func(entry metaCacheEntry)
+
+	// partial will be returned when there is disagreement between disks.
+	// if disk did not return any result, but also haven't errored
+	// the entry will be empty and errs will
+	partial func(entries metaCacheEntries, nAgreed int, errs []error)
+
+	// finished will be called when all streams have finished and
+	// more than one disk returned an error.
+	// Will not be called if everything operates as expected.
+	finished func(errs []error)
+}
+
+// listPathRaw will list a path on the provided drives.
+// See listPathRawOptions on how results are delivered.
+// Directories are always returned.
+// Cache will be bypassed.
+// Context cancellation will be respected but may take a while to effectuate.
+func listPathRaw(ctx context.Context, opts listPathRawOptions) (err error) {
+	disks := opts.disks
+	if len(disks) == 0 {
+		return fmt.Errorf("listPathRaw: 0 drives provided")
+	}
+
+	// Disconnect from call above, but cancel on exit.
+	ctx, cancel := context.WithCancel(GlobalContext)
+	defer cancel()
+
+	askDisks := len(disks)
+	var readers = make([]*metacacheReader, askDisks)
+	for i := range disks {
+		r, w := io.Pipe()
+		d := disks[i]
+		readers[i], err = newMetacacheReader(r)
+		if err != nil {
+			return err
+		}
+		// Send request to each disk.
+		go func() {
+			err := d.WalkDir(ctx, WalkDirOptions{
+				Bucket:         opts.bucket,
+				BaseDir:        opts.path,
+				Recursive:      opts.recursive,
+				ReportNotFound: opts.reportNotFound,
+				FilterPrefix:   opts.filterPrefix}, w)
+			w.CloseWithError(err)
+			if err != io.EOF {
+				logger.LogIf(ctx, err)
+			}
+		}()
+	}
+
+	topEntries := make(metaCacheEntries, len(readers))
+	errs := make([]error, len(readers))
+	for {
+		// Get the top entry from each
+		var current metaCacheEntry
+		var atEOF, fnf, hasErr, agree int
+		for i := range topEntries {
+			topEntries[i] = metaCacheEntry{}
+		}
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		default:
+		}
+		for i, r := range readers {
+			if errs[i] != nil {
+				hasErr++
+				continue
+			}
+			entry, err := r.peek()
+			switch err {
+			case io.EOF:
+				atEOF++
+				continue
+			case nil:
+			default:
+				if err.Error() == errFileNotFound.Error() {
+					atEOF++
+					fnf++
+					continue
+				}
+
+				hasErr++
+				errs[i] = err
+				continue
+			}
+			// If no current, add it.
+			if current.name == "" {
+				topEntries[i] = entry
+				current = entry
+				agree++
+				continue
+			}
+			// If exact match, we agree.
+			if current.matches(&entry, opts.bucket) {
+				topEntries[i] = entry
+				agree++
+				continue
+			}
+			// If only the name matches we didn't agree, but add it for resolution.
+			if entry.name == current.name {
+				topEntries[i] = entry
+				continue
+			}
+			// We got different entries
+			if entry.name > current.name {
+				continue
+			}
+			// We got a new, better current.
+			// Clear existing entries.
+			for i := range topEntries[:i] {
+				topEntries[i] = metaCacheEntry{}
+			}
+			agree = 1
+			current = entry
+			topEntries[i] = entry
+		}
+
+		// Stop if we exceed number of bad disks
+		if hasErr > len(disks)-opts.minDisks && hasErr > 0 {
+			if opts.finished != nil {
+				opts.finished(errs)
+			}
+			var combinedErr []string
+			for i, err := range errs {
+				if err != nil {
+					combinedErr = append(combinedErr, fmt.Sprintf("disk %d returned: %s", i, err))
+				}
+			}
+			return errors.New(strings.Join(combinedErr, ", "))
+		}
+
+		// Break if all at EOF or error.
+		if atEOF+hasErr == len(readers) {
+			if hasErr > 0 && opts.finished != nil {
+				opts.finished(errs)
+			}
+			break
+		}
+		if fnf == len(readers) {
+			return errFileNotFound
+		}
+		if agree == len(readers) {
+			// Everybody agreed
+			for _, r := range readers {
+				r.skip(1)
+			}
+			if opts.agreed != nil {
+				opts.agreed(current)
+			}
+			continue
+		}
+		if opts.partial != nil {
+			opts.partial(topEntries, agree, errs)
+		}
+		// Skip the inputs we used.
+		for i, r := range readers {
+			if topEntries[i].name != "" {
+				r.skip(1)
+			}
+		}
+	}
+	return nil
+}

cmd/metacache-walk.go

@@ -43,6 +43,9 @@ type WalkDirOptions struct {
 	// Do a full recursive scan.
 	Recursive bool
 
+	// ReportNotFound will return errFileNotFound if all disks reports the BaseDir cannot be found.
+	ReportNotFound bool
+
 	// FilterPrefix will only return results with given prefix within folder.
 	// Should never contain a slash.
 	FilterPrefix string
@@ -98,6 +101,9 @@ func (s *xlStorage) WalkDir(ctx context.Context, opts WalkDirOptions, wr io.Writ
 			if err != errVolumeNotFound && err != errFileNotFound {
 				logger.LogIf(ctx, err)
 			}
+			if opts.ReportNotFound && err == errFileNotFound && current == opts.BaseDir {
+				return errFileNotFound
+			}
 			// Forward some errors?
 			return nil
 		}