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:
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