[linux-lvm] Running thin_trim before activating a thin pool

[Zdenek Kabelac]

Dne 31. 01. 22 v 12:02 Gionatan Danti napsal(a):
> Il 2022-01-29 18:45 Demi Marie Obenour ha scritto:
>> Is it possible to configure LVM2 so that it runs thin_trim before it
>> activates a thin pool?  Qubes OS currently runs blkdiscard on every thin
>> volume before deleting it, which is slow and unreliable.  Would running
>> thin_trim during system startup provide a better alternative?
> 
> I think that, if anything, it would be worse: a long discard during boot can 
> be problematic, even leading to timeout on starting other services.
> After all, blkdiscard should be faster then something done at higher level.
> 
> That said, I seem to remember that deleting a fat volume should automatically 
> trim/discard it if issue_discard=1. Is this not true for thin volumes?


'issue_discard' relates only to the internal lvm2 logic when some extents 
become free for reuse (so i.e. after 'lvremove/lvreduce/vgremove...'.

However since with thin volumes no physical extents of VG are released (as the 
thin volume is releasing chunks from the thin-pool) - there is no discard 
issued by lvm.

Regards

Zdenek