Releasing deleted blocks from a sparse ZVOL

[Paul Esson]

Hi Eric,
Thanks for your feedback which sounds encouraging. I'll give that a try.

Regards,
Paul.E


Paul Esson | Redstor Limited
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________________________________
From: eborisch at alumni.stanford.edu <eborisch at alumni.stanford.edu> on behalf of Eric Borisch <eborisch at gmail.com>
Sent: Monday, May 14, 2018 9:37:43 PM
To: Karli Sjöberg
Cc: Paul Esson; freebsd-fs at freebsd.org
Subject: Re: Releasing deleted blocks from a sparse ZVOL

I've had success in a similar config by attaching the zvol as 'ahci-hd', which shows up as a 'BHYVE SATA DISK' in a BSD guest. With such a guest (running a zpool on the attached device):

kstat.zfs.misc.zio_trim.failed: 0
kstat.zfs.misc.zio_trim.unsupported: 0
kstat.zfs.misc.zio_trim.success: 179883
kstat.zfs.misc.zio_trim.bytes: 13126696960

Also working with a linux guest.

I see the expected tracking of the 'logicalreferenced' size in the host with the ALLOC size in the guest (allowing for upward bias due to using 32k sector sizes on my zvols).

Note that TRIM and UNMAP are two extremely similar but distinct (used for SATA & SCSI, respectively) commands. Both are commonly referred to as 'trim' by layers above the device drivers.

  - Eric