----- Original Message -----
From: "Slawa Olhovchenkov" <s...@zxy.spb.ru>
To: "Steven Hartland" <s...@freebsd.org>
Cc: <src-committ...@freebsd.org>; <svn-src-all@freebsd.org>;
<svn-src-h...@freebsd.org>
Sent: Sunday, September 07, 2014 5:01 PM
Subject: Re: svn commit: r256956 - in head/sys: cam/ata cam/scsi cddl/contrib/opensolaris/uts/common/fs/zfs
cddl/contrib/opensolaris/uts/common/fs/zfs/sys geom sys
On Wed, Oct 23, 2013 at 09:54:59AM +0000, Steven Hartland wrote:
Author: smh
Date: Wed Oct 23 09:54:58 2013
New Revision: 256956
URL: http://svnweb.freebsd.org/changeset/base/256956
Log:
Improve ZFS N-way mirror read performance by using load and locality
information.
The existing algorithm selects a preferred leaf vdev based on offset of the
zio
request modulo the number of members in the mirror. It assumes the devices are
of equal performance and that spreading the requests randomly over both drives
will be sufficient to saturate them. In practice this results in the leaf
vdevs
being under utilized.
The new algorithm takes into the following additional factors:
* Load of the vdevs (number outstanding I/O requests)
* The locality of last queued I/O vs the new I/O request.
Within the locality calculation additional knowledge about the underlying vdev
is considered such as; is the device backing the vdev a rotating media device.
This results in performance increases across the board as well as significant
increases for predominantly streaming loads and for configurations which don't
have evenly performing devices.
The following are results from a setup with 3 Way Mirror with 2 x HD's and
1 x SSD from a basic test running multiple parrallel dd's.
With pre-fetch disabled (vfs.zfs.prefetch_disable=1):
== Stripe Balanced (default) ==
Read 15360MB using bs: 1048576, readers: 3, took 161 seconds @ 95 MB/s
== Load Balanced (zfslinux) ==
Read 15360MB using bs: 1048576, readers: 3, took 297 seconds @ 51 MB/s
== Load Balanced (locality freebsd) ==
Read 15360MB using bs: 1048576, readers: 3, took 54 seconds @ 284 MB/s
With pre-fetch enabled (vfs.zfs.prefetch_disable=0):
== Stripe Balanced (default) ==
Read 15360MB using bs: 1048576, readers: 3, took 91 seconds @ 168 MB/s
== Load Balanced (zfslinux) ==
Read 15360MB using bs: 1048576, readers: 3, took 108 seconds @ 142 MB/s
== Load Balanced (locality freebsd) ==
Read 15360MB using bs: 1048576, readers: 3, took 48 seconds @ 320 MB/s
In addition to the performance changes the code was also restructured, with
the help of Justin Gibbs, to provide a more logical flow which also ensures
vdevs loads are only calculated from the set of valid candidates.
The following additional sysctls where added to allow the administrator
to tune the behaviour of the load algorithm:
* vfs.zfs.vdev.mirror.rotating_inc
* vfs.zfs.vdev.mirror.rotating_seek_inc
* vfs.zfs.vdev.mirror.rotating_seek_offset
* vfs.zfs.vdev.mirror.non_rotating_inc
* vfs.zfs.vdev.mirror.non_rotating_seek_inc
These changes where based on work started by the zfsonlinux developers:
https://github.com/zfsonlinux/zfs/pull/1487
Reviewed by: gibbs, mav, will
MFC after: 2 weeks
Sponsored by: Multiplay
No MFC yet.
Grr not seen any MFC reminder :( Will send a request to re@ for permission
along with r260713.
Regards
Steve
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