Date: Fri, 14 May 2021 14:27:05 +0200 From: Stefan Esser <se@freebsd.org> To: Pete French <petefrench@ingresso.co.uk> Cc: stable@freebsd.org Subject: Re: Does FreeBSD 13 disable the VEV cache in ZFS ? Message-ID: <44b0243a-45b6-d098-948b-a6f3d6a53ba7@freebsd.org> In-Reply-To: <E1lhTHC-000NAw-Oo@dilbert.ingresso.co.uk> References: <E1lhTHC-000NAw-Oo@dilbert.ingresso.co.uk>
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This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --0mdWVhfS9OcRv2Gkf4Yd27ESgE5UauhwN Content-Type: multipart/mixed; boundary="LpRLxRJNo09ZcGQLiIj1QqFlTNRKMRbGx"; protected-headers="v1" From: Stefan Esser <se@freebsd.org> To: Pete French <petefrench@ingresso.co.uk> Cc: stable@freebsd.org Message-ID: <44b0243a-45b6-d098-948b-a6f3d6a53ba7@freebsd.org> Subject: Re: Does FreeBSD 13 disable the VEV cache in ZFS ? References: <E1lhTHC-000NAw-Oo@dilbert.ingresso.co.uk> In-Reply-To: <E1lhTHC-000NAw-Oo@dilbert.ingresso.co.uk> --LpRLxRJNo09ZcGQLiIj1QqFlTNRKMRbGx Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: quoted-printable Am 14.05.21 um 10:34 schrieb Pete French: >=20 > Am just upgrading my machiens, and have noticed an oddity. > This is on a machine runnign 12.2 >=20 > # zfs-stats -D >=20 > -----------------------------------------------------------------------= - > ZFS Subsystem Report Fri May 14 08:30:50 2021 > -----------------------------------------------------------------------= - >=20 > VDEV Cache Summary: 88.31 m > Hit Ratio: 31.20% 27.55 m > Miss Ratio: 68.48% 60.47 m > Delegations: 0.32% 284.97 k >=20 > -----------------------------------------------------------------------= - >=20 >=20 > This is on a machine running 13.0 >=20 > # zfs-stats -D >=20 > -----------------------------------------------------------------------= - > ZFS Subsystem Report Fri May 14 08:32:18 2021 > -----------------------------------------------------------------------= - >=20 > VDEV cache is disabled >=20 > -----------------------------------------------------------------------= - >=20 > Same config on both. So, is it really disabled, or is zfs-stats getting= this > wrong for some reason ? I cant find any refernbce to this in the releas= e notes > or by googling. Hi Pete, zfs-stats has last been modified by me to make it work with the sysctl na= mes changed by OpenZFS. (But I might have missed a few ...) Could you check the values of the following sysctl variables: vfs.zfs.vdev.cache_size vfs.zfs.vdev.cache_bshift vfs.zfs.vdev.cache_max kstat.zfs.misc.vdev_cache_stats.misses kstat.zfs.misc.vdev_cache_stats.hits kstat.zfs.misc.vdev_cache_stats.delegations On my system, vfs.zfs.vdev.cache_size is always 0 - and that results in t= he message "VDEV cache is disabled" that you got, too. And I'd guess that th= e kstat variables will all report 0, too (not surprising if the size is 0).= A quick web search reveals: https://openzfs.github.io/openzfs-docs/Performance%20and%20Tuning/Module%= 20Parameters.html#zfs-vdev-cache-size Quote: Note: with the current ZFS code, the vdev cache is not helpful and in som= e cases actually harmful. Thus it is disabled by setting the zfs_vdev_cache= _size =3D 0 You may want to try setting "vfs.zfs.vdev.cache_size" (name changed, it u= sed to be cache.size instead of cache_size) in /boot/loader.conf and perform = a few performance tests. (I have not verified that the current implementati= on actually uses and supports a value specified that way, though.) Regards, STefan --LpRLxRJNo09ZcGQLiIj1QqFlTNRKMRbGx-- --0mdWVhfS9OcRv2Gkf4Yd27ESgE5UauhwN Content-Type: application/pgp-signature; name="OpenPGP_signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="OpenPGP_signature" -----BEGIN PGP SIGNATURE----- wsB5BAABCAAjFiEEo3HqZZwL7MgrcVMTR+u171r99UQFAmCebJkFAwAAAAAACgkQR+u171r99UQ7 NggAg7Srre02gZmUnUfeENKedoDwpiespWqrDzsEHTbninv+ddnSZvjQoyat9Mp6U5pcexwaxtwl eYLMt3LuIEP9TUJXtG1UIdCMnXrhkW/yEoi3d8z+QvTvSnYQhLovP4R9ssIzI+GqEtzk2WMw+YXQ /VTHYb2UVejJ3mRB1biKbQlvctOweDRP+2NB7FN+Th/OfROJIPXTs+SZWeGdbuCYdG6qBFpIDlvU CMprzW7z5b4ctIeC3/N5FF2DOI2Ibmotm2E0EvcmPXw5zWEJonqAROXm/uMeuKymh3kpo82LknWF iPAyKJO5dw1wJ+x8QrwQZi3Eaoh4yt7cMcescbMzQw== =joTH -----END PGP SIGNATURE----- --0mdWVhfS9OcRv2Gkf4Yd27ESgE5UauhwN--
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