Cannot remove Snapshot. Low disk space on target Storage Domain
I am in shock.
I have a storage domain with 500 GB total, 121 GB available. And I have a thin provisioned virtual disk with 200 GB used and allocated, plus a snapshot I took last week before some upgrades at about 40 GB. The upgrade is done, now it's time to remove the snapshot. This fails with:
Cannot remove Snapshot. Low disk space on target Storage Domain
Looking at this article:
https://access.redhat.com/solutions/897013
I apparently need (original disk size + snapshot size) free space in the LUN to get rid of a snapshot????
The article says, "So in actual no data is removed..." This cannot be true. The snapshot contains old copies of blocks replaced by new copies of blocks. Removing a snapshot gets rid of old copies of blocks. So by definition, lots of data is removed.
If I'm reading the article correctly, the real issue is, snapshot removal is wildly, insanely inefficient because it makes a whole new copy of all the blocks. To delete this snapshot, I will need to provision a whole new LUN with 500+ GB of storage, copy my virtual disks to it, then remove the snapshot. And I may need to do all this with my VM - my company email server - down. And this only works if I have enough SAN space to handle something like 2.5X of what I'm actually using. If I am low on SAN space, I'm stuck with this snapshot forever. I can never get rid of it because I don't have anywhere to put the new merged virtual disk.
And it gets worse. I can find no documentation about this behavior in any of the standard docs - only in articles I stumble across after I run into the problem.
I'm not happy. C'mon guys, you gotta do better than that.
- Greg Scott
Responses
Dear Greg,
I totally agree with you on the need to reflect the storage needs of merge operation.
Rather than documenting this, which you suggested, I'd go with a warning dialogue implementation
that would display pre-calculated storage requirements to users so that they could review it and
proactively act before actual run of the merge operation.
I filed following bug report to track this: https://bugzilla.redhat.com/show_bug.cgi?id=1117231
Thank you very much for valuable feedback. Do not hesitate contacting Red Hat support in case you wish
to keep track on progress of the bug via a support case.
Kind regards
Tomas Dosek
Senior Software Maintenance Engineer - Virtualization
I am now running into this issue.
I have a storage domain of 1 TB, with a VM disk of 500 GB with one snapshot. I guess this means that even if I manage to free the domain of everything else, I still won't be able to remove the snapshot without adding extra storage.
The strange thing is, that this VM disk used to have two snapshots, one of which cannot be removed due to insufficient space, but the other one could in fact be removed without error, even though it took 13,5 hours. How is that even possible, considering that there was only about 100 GB available?
Cheers,
Martijn.
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