Date: Tue, 8 Sep 2020 13:52:34 -0400 From: Allan Jude <allanjude@freebsd.org> To: freebsd-fs@freebsd.org Subject: Re: OpenZFS and L2ARC Message-ID: <4f30a8a5-b7fb-e4bb-a5e6-b59fa4ec10c2@freebsd.org> In-Reply-To: <b8f63e55-4c7e-8be0-7c52-5d8e6cb333f4@freebsd.org> References: <b8f63e55-4c7e-8be0-7c52-5d8e6cb333f4@freebsd.org>
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This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --BHIyuXEo77xdHCnTHZ5IPrjW2EOEbP8XD Content-Type: multipart/mixed; boundary="m4BJR1mD8qd0ajS7YJhMBnWcxgtMpCAfA"; protected-headers="v1" From: Allan Jude <allanjude@freebsd.org> To: freebsd-fs@freebsd.org Message-ID: <4f30a8a5-b7fb-e4bb-a5e6-b59fa4ec10c2@freebsd.org> Subject: Re: OpenZFS and L2ARC References: <b8f63e55-4c7e-8be0-7c52-5d8e6cb333f4@freebsd.org> In-Reply-To: <b8f63e55-4c7e-8be0-7c52-5d8e6cb333f4@freebsd.org> --m4BJR1mD8qd0ajS7YJhMBnWcxgtMpCAfA Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 2020-09-08 03:43, Stefan Esser wrote: > OpenZFS seems to work quite well for me, in general, but I have > questions regarding the L2ARC statistics. >=20 > The system uses a 3 * 6 TB raidz1 (plus further ZFS volumes that > are not relevant here, since without level 2 ARC) and an 1 TB M.2 > SSD with a 256 GB partition for the L2ARC (and most of it currently > unused, else). >=20 > The L2ARC seems to have filled to the limit of 256 GB, but after > several reboots, sysctl reports a L2ARC size of nearly twice the > allocated space: >=20 > kstat.zfs.misc.arcstats.l2_size: 534620858880 >=20 > That is 497 GiB, and might be possible with a lz4 compression > factor of 2 - if the value reported is not the space allocated, > but the actual (uncompressed) data held by the L2ARC. >=20 >=20 > The sysutils/zfs-stats port reports the following values for > this system, BTW: >=20 > -----------------------------------------------------------------------= - > ZFS Subsystem Report=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 Tue S= ep=A0 8 09:02:46 2020 > -----------------------------------------------------------------------= - >=20 > L2 ARC Summary: (HEALTHY) > =A0=A0=A0=A0Passed Headroom:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 0 > =A0=A0=A0=A0Tried Lock Failures:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 0 > =A0=A0=A0=A0IO In Progress:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= 0 > =A0=A0=A0=A0Low Memory Aborts:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 7 > =A0=A0=A0=A0Free on Write:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= 123 > =A0=A0=A0=A0Writes While Full:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 0 > =A0=A0=A0=A0R/W Clashes:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 0= > =A0=A0=A0=A0Bad Checksums:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= 0 > =A0=A0=A0=A0IO Errors:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 0 > =A0=A0=A0=A0SPA Mismatch:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 = 0 >=20 > L2 ARC Size: (Adaptive)=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 49= 7.91=A0=A0=A0 GiB > =A0=A0=A0=A0Header Size:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 0.11%=A0=A0=A0= 558.83=A0=A0=A0 MiB >=20 > L2 ARC Evicts: > =A0=A0=A0=A0Lock Retries:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 = 6 > =A0=A0=A0=A0Upon Reading:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 = 0 >=20 > L2 ARC Breakdown:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 5.75=A0=A0= =A0 m > =A0=A0=A0=A0Hit Ratio:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 81.94%=A0=A0=A0= 4.71=A0=A0=A0 m > =A0=A0=A0=A0Miss Ratio:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 18.06%=A0=A0=A0= 1.04=A0=A0=A0 m > =A0=A0=A0=A0Feeds:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0 235.04=A0=A0=A0 k >=20 > L2 ARC Buffer: > =A0=A0=A0=A0Bytes Scanned:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= 0=A0=A0=A0 Bytes > =A0=A0=A0=A0Buffer Iterations:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 0 > =A0=A0=A0=A0List Iterations:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 0 > =A0=A0=A0=A0NULL List Iterations:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 0 >=20 > L2 ARC Writes: > =A0=A0=A0=A0Writes Sent:=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 100.00%=A0=A0= =A0 22.67=A0=A0=A0 k >=20 > -----------------------------------------------------------------------= - >=20 > With the FreeBSD ZFS (without persistent L2ARC) I never got more > than 20% hit ratio on the L2ARC between reboots. >=20 > Quite a number of sysctl variable names have changed, and the port > needs to be adapted to the new names (therefore there are lots of 0 > values in the -L output). >=20 > The following names used by zfs-stats do not exist in OpenZFS: >=20 > kstat.zfs.misc.arcstats.recycle_miss > kstat.zfs.misc.arcstats.l2_write_buffer_bytes_scanned > kstat.zfs.misc.arcstats.l2_write_buffer_iter > kstat.zfs.misc.arcstats.l2_write_buffer_list_iter > kstat.zfs.misc.arcstats.l2_write_buffer_list_null_iter > kstat.zfs.misc.arcstats.l2_write_full > kstat.zfs.misc.arcstats.l2_write_in_l2 > kstat.zfs.misc.arcstats.l2_write_io_in_progress > kstat.zfs.misc.arcstats.l2_write_not_cacheable > kstat.zfs.misc.arcstats.l2_write_passed_headroom > kstat.zfs.misc.arcstats.l2_write_pios > kstat.zfs.misc.arcstats.l2_write_spa_mismatch > kstat.zfs.misc.arcstats.l2_write_trylock_fail > kstat.zfs.misc.arcstats.l2_writes_hdr_miss > vfs.zfs.vdev.cache.size >=20 > The existence of vfs.zfs.vdev.cache.size vs vfs.zfs.vdev.cache_size > can be used to detect OpenZFS, and is easily fixed. >=20 > But the above listed L2ARC values seem to have been removed from or > have never existed in OpenZFS, and I did not find any substitutes. >=20 > Are there any plans to re-create them in OpenZFS on FreeBSD or are > they gone for good? >=20 > I'd like to update the zfs-stats port for compatibil=EDty with OpenZFS = =2E.. > _______________________________________________ > freebsd-fs@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-fs > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org" I think the kstats you are looking for are: kstat.zfs.misc.arcstats.l2_asize: 0 kstat.zfs.misc.arcstats.l2_size: 0 l2_asize is the 'allocated' size, that will be how much actual disk space is used. And l2_size will be the amount of data contained, so compression may make this quite a bit larger than the size of the physical device. --=20 Allan Jude --m4BJR1mD8qd0ajS7YJhMBnWcxgtMpCAfA-- --BHIyuXEo77xdHCnTHZ5IPrjW2EOEbP8XD Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (MingW32) iQIcBAEBAgAGBQJfV8TjAAoJEBmVNT4SmAt+UsAQAMHOPL/VVqRg1UlNzlHWR5MB aAALic6r+kRG1uI2sFHuLJFEW0KDNmSV0wS2yZGIoXdmEmGSGtk2vPZtdMGW8e4Y BCNY36zCaC9HPc5R6nL+PFdV2U0CU46WEtCQy51ESotjQxNR+EkVnETuRLyaDTMY vqAgs33ue/fVKSot8UfgYedjJlT8F1CtRGuby3cClZUr7HmBesJrstZoIv+0NJ8H MQhGhOvuSeeLQz81LOVsC9nj1PcAtAHBJbbffAhC0wLh6rQC92OaFNUQFj+4BXpm 7w3JzAbUi/+MpY8xIFNkxuYAQ9ve3KBAy7EtHFWY/vCNZIkoM8XSuCPilFFXiNLE paqZ2WCutckXpc5J3lYZIFWiEMgjuSUhut5IZaGd0CBa4AqGT2q1BPFxMndLehaP b5Aq8cAKIKRxL3++6vQgO7KUVAF2QBcrkI6GSUd5stE7NKPqi+5panCkQwd5AGFP NFSAfNIQrKQ3bl0pVq3oyPnxjTsnKvlpvRLXsJZhZC99jxx7qa+eXyUdr1HC9kLy VnP5sd3Xk37lce5UnQKa+pLHkR5JrWmvPiHXT24+aQJxhZfI546qfdOFnztzs68Z iJAYXAy7qINXRIscc0ytiaSabr77dlvgBAIkCu6VGrhAZMLQtgnh5nr6fXeND81W IG3TavEXUNFKfXSByYwn =YTk9 -----END PGP SIGNATURE----- --BHIyuXEo77xdHCnTHZ5IPrjW2EOEbP8XD--
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