Fix handling of fixed read-only volumes for `volume.check.disk`.

There's unfortunatley no way to tell whether a volume is flagged read-only
because it got full, or because it is faulty. To address this, modify the
check logic so all read-only volumes are processed; if no changes are written
(i.e. the volume is healthy) it is kept as read-only.

Volumes which are modified in this process are deemed fixed, and switched to writable.

weed/shell/command_volume_check_disk.go

@@ -64,9 +64,9 @@ func (c *commandVolumeCheckDisk) Help() string {
 			append entries in B and not in A to A
 
 	optionally, for each non-writable volume replica A
-		if volume is not full
+		select a writable volume replica B
+		if entries in A don't match B
 			prune late volume entries not matching its index file
-			select a writable volume replica B
 			append missing entries from B into A
 			mark the volume as writable (healthy)
 
@@ -179,9 +179,16 @@ func (vcd *volumeCheckDisk) checkWritableVolumes(volumeReplicas map[uint32][]*Vo
 				writableReplicas = append(writableReplicas[:1], writableReplicas[2:]...)
 				continue
 			}
-			if err := vcd.syncTwoReplicas(a, b, true); err != nil {
-				vcd.write("sync volume %d on %s and %s: %v", a.info.Id, a.location.dataNode.Id, b.location.dataNode.Id, err)
+
+			modified, err := vcd.syncTwoReplicas(a, b, true)
+			if err != nil {
+				vcd.write("failed to sync volumes %d on %s and %s: %v", a.info.Id, a.location.dataNode.Id, b.location.dataNode.Id, err)
+			} else {
+				if modified {
+					vcd.write("synced %s and %s for volume %d", a.location.dataNode.Id, b.location.dataNode.Id, a.info.Id)
+				}
 			}
+
 			// always choose the larger volume to be the source
 			if a.info.FileCount > b.info.FileCount {
 				writableReplicas = append(writableReplicas[:1], writableReplicas[2:]...)
@@ -280,19 +287,25 @@ func (vcd *volumeCheckDisk) checkReadOnlyVolumes(volumeReplicas map[uint32][]*Vo
 					return err
 				}
 
-				// ...fix it...
-				// TODO: test whether syncTwoReplicas() is enough to prune garbage entries on broken volumes.
-				if err := vcd.syncTwoReplicas(source, r, false); err != nil {
-					vcd.write("sync read-only volume %d on %s from %s: %v\n", vid, r.location.dataNode.Id, source.location.dataNode.Id, err)
+				// ...try to fix it...
+				// TODO: test whether syncTwoReplicas() is enough to prune garbage entries on broken volumes...
+				modified, err := vcd.syncTwoReplicas(source, r, false)
+				if err != nil {
+					vcd.write("sync read-only volume %d on %s from %s: %v", vid, r.location.dataNode.Id, source.location.dataNode.Id, err)
 
-					// ...or revert it back to read-only, if something went wrong.
-					// TODO: we should keep unchanged volumes as read-only, so we don't modify valid volumes which are full.
 					if roErr := vcd.makeVolumeReadonly(vid, r); roErr != nil {
-						return fmt.Errorf("failed to make volume %d on %s readonly after: %v: %v", vid, r.location.dataNode.Id, err, roErr)
+						return fmt.Errorf("failed to revert volume %d on %s to readonly after: %v: %v", vid, r.location.dataNode.Id, err, roErr)
 					}
-					vcd.write("volume %d on %s is now read-only\n", vid, r.location.dataNode.Id)
-
 					return err
+				} else {
+					if modified {
+						vcd.write("volume %d on %s is now synced to %d and writable", vid, r.location.dataNode.Id, source.location.dataNode.Id)
+					} else {
+						// ...or restore back to read-only, if no changes were made.
+						if err := vcd.makeVolumeReadonly(vid, r); err != nil {
+							return fmt.Errorf("failed to revert volume %d on %s to readonly: %v", vid, r.location.dataNode.Id, err)
+						}
+					}
 				}
 
 				return nil
@@ -411,35 +424,39 @@ func (vcd *volumeCheckDisk) shouldSkipVolume(a, b *VolumeReplica) (bool, error)
 
 // syncTwoReplicas attempts to sync all entries from a source volume replica into a target. If bi-directional mode
 // is enabled, changes from target are also synced back into the source.
-func (vcd *volumeCheckDisk) syncTwoReplicas(source, target *VolumeReplica, bidi bool) (err error) {
+// Returns true if source and/or target were modified, false otherwise.
+func (vcd *volumeCheckDisk) syncTwoReplicas(source, target *VolumeReplica, bidi bool) (modified bool, err error) {
 	sourceHasChanges, targetHasChanges := true, true
 	const maxIterations = 5
 	iteration := 0
 
+	modified = false
+
 	for (sourceHasChanges || targetHasChanges) && iteration < maxIterations {
 		iteration++
 		vcd.writeVerbose("sync iteration %d/%d for volume %d", iteration, maxIterations, source.info.Id)
 
 		prevSourceHasChanges, prevTargetHasChanges := sourceHasChanges, targetHasChanges
 		if sourceHasChanges, targetHasChanges, err = vcd.checkBoth(source, target, bidi); err != nil {
-			return err
+			return modified, err
 		}
+		modified = modified || sourceHasChanges || targetHasChanges
 
 		// Detect if we're stuck in a loop with no progress
 		if iteration > 1 && prevSourceHasChanges == sourceHasChanges && prevTargetHasChanges == targetHasChanges && (sourceHasChanges || targetHasChanges) {
 			vcd.write("volume %d sync is not making progress between %s and %s after iteration %d, stopping to prevent infinite loop",
 				source.info.Id, source.location.dataNode.Id, target.location.dataNode.Id, iteration)
-			return fmt.Errorf("sync not making progress after %d iterations", iteration)
+			return modified, fmt.Errorf("sync not making progress after %d iterations", iteration)
 		}
 	}
 
 	if iteration >= maxIterations && (sourceHasChanges || targetHasChanges) {
 		vcd.write("volume %d sync reached maximum iterations (%d) between %s and %s, may need manual intervention",
 			source.info.Id, maxIterations, source.location.dataNode.Id, target.location.dataNode.Id)
-		return fmt.Errorf("reached maximum sync iterations (%d)", maxIterations)
+		return modified, fmt.Errorf("reached maximum sync iterations (%d)", maxIterations)
 	}
 
-	return nil
+	return modified, nil
 }
 
 // checkBoth performs a sync between source and target volume replicas. If bi-directional mode is enabled, changes from target are also synced back into the source.
@@ -628,7 +645,7 @@ func (vcd *volumeCheckDisk) copyVolumeIndexFile(collection string, volumeId uint
 
 		copyFileClient, err := volumeServerClient.CopyFile(context.Background(), &volume_server_pb.CopyFileRequest{
 			VolumeId:                 volumeId,
-			Ext:                      ".idx",
+			Ext:                      ext,
 			CompactionRevision:       math.MaxUint32,
 			StopOffset:               math.MaxInt64,
 			Collection:               collection,