Snapshots that won't delete [was: Re: ZFS on root booting...]

[Shane Ambler]

On 11/09/2014 16:42, Ben Morrow wrote:
> Quoth Adam McDougall <mcdouga9 at egr.msu.edu>:
>>
>> Were you running a newer kernel with an older format zpool?  I heard
>> ixsystems had customers doing that and ran into corruption when they
>> tried to modify the zpool in some way (expand? I don't remember).
>> http://www.bsdnow.tv/episodes/2014_07_09-zfs_war_stories
> 
> Oh! Might this be what's causing a problem I've been meaning to ask
> about?
> 
> My desktop at home is running (a patched, but not anywhere to do with
> ZFS) 10-STABLE from a while ago, with a zpool that was created under
> 8.2-R and is still at version 15. I have been deliberately not upgrading
> it, because I saw no reason to and it seemed safer to leave things as
> they were.
> 
> Recently, though, my dump script has started having occasional problems
> with snapshots that won't delete. Pending further investigation I have
> been renaming them to allow the recursive delete to succeed, and (so
> far) rebooting has always made it possible to get rid of them. 

I have seen that issue with 9.2 and at least one other person mentioned
it as well. I currently have a snapshot that I accessed at least 3 weeks
ago and renamed to keep rotations working and have not accessed since,
it still won't delete as it is busy. I can only delete these snapshots
after a reboot.

The only cause I know is accessing the snapshot.
I can simply ls .zfs/snapshot/daily.01/somefolder to prevent it being
deleted. With a manual zfs destroy I get "dataset is busy" and have not
found a way to find any process that has hold of it.

It seems that some aging of the snapshot needs to happen. Testing a
rotate, access, rotate keeps working ok, but access last nights
snapshot and then rotate and it blocks.

I'm fairly sure that I was running 9.1 when I created this zpool and
then later upgraded to 9.2. zpool upgrade says "This system supports
ZFS pool feature flags" and "Pool 'zrpleader' already has all supported
features enabled".

-- 
FreeBSD - the place to B...Serving Data

Shane Ambler