[ceph-users] Can not delete snapshot with "ghost" children

Valery Tschopp valery.tschopp at switch.ch
Thu Nov 30 02:11:39 PST 2017


We've a problem to delete a snapshot. There was a child image of the 
snapshot, but the child image was flatten. And now the snapshot still 
"think" it has children, and can not be deleted.

Snapshot and children:

$ rbd snap ls volumes/volume-49ccf5a6-4c17-434a-a087-f04acef978ef
SNAPID NAME                                              SIZE
  94183 snapshot-376e23d6-e723-4dbb-b558-174b275244b5 40960 MB

$ rbd children 
volumes/volume-49ccf5a6-4c17-434a-a087-f04acef978ef at snapshot-376e23d6-e723-4dbb-b558-174b275244b5

Child image (was flatten, and now is without parent):

$ rbd info volumes/volume-a86350ad-2d4e-4863-bff3-67304b4b7b3c
rbd image 'volume-a86350ad-2d4e-4863-bff3-67304b4b7b3c':
	size 40960 MB in 10240 objects
	order 22 (4096 kB objects)
	block_name_prefix: rbd_data.1d4f6a3cd198f8
	format: 2
	features: layering, exclusive-lock, object-map

When I try to delete the snapshot, ceph tells me that the snapshot is 
protected. And when I try to unprotect it, it fails telling me there is 
still a child!?!?

$ rbd snap rm 
volumes/volume-49ccf5a6-4c17-434a-a087-f04acef978ef at snapshot-376e23d6-e723-4dbb-b558-174b275244b5
rbd: snapshot 'snapshot-376e23d6-e723-4dbb-b558-174b275244b5' is 
protected from removal.
2017-11-30 11:09:31.054416 7fe80e8f9100 -1 librbd::Operations: snapshot 
is protected

$ rbd snap unprotect 
volumes/volume-49ccf5a6-4c17-434a-a087-f04acef978ef at snapshot-376e23d6-e723-4dbb-b558-174b275244b5
2017-11-30 11:09:56.899548 7fc6432cd700 -1 
librbd::SnapshotUnprotectRequest: cannot unprotect: at least 1 
child(ren) [1d4f6a3cd198f8] in pool 'volumes'
2017-11-30 11:09:56.899578 7fc6432cd700 -1 
librbd::SnapshotUnprotectRequest: encountered error: (16) Device or 
resource busy
2017-11-30 11:09:56.899588 7fc6432cd700 -1 
librbd::SnapshotUnprotectRequest: 0xab0d918540 should_complete_error: 
2017-11-30 11:09:56.902702 7fc6432cd700 -1 
librbd::SnapshotUnprotectRequest: 0xab0d918540 should_complete_error: 
rbd: unprotecting snap failed: (16) Device or resource busy

How can we solve this issue?


Valéry Tschopp, Software Engineer
Werdstrasse 2, P.O. Box, 8021 Zurich, Switzerland
email: valery.tschopp at switch.ch phone: +41 44 268 1544

30 years of pioneering the Swiss Internet.
Celebrate with us at https://swit.ch/30years

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