Date: Tue, 26 Apr 2016 17:26:53 -0500 From: "Eric A. Borisch" <eborisch@gmail.com> To: Miroslav Lachman <000.fbsd@quip.cz> Cc: "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org> Subject: Re: How to speed up slow zpool scrub? Message-ID: <CAASnNnowU0he_2BFqkb-ZTNBVn00wc8Qt7CWSPVQT%2BuCKaJSKg@mail.gmail.com> In-Reply-To: <571F62AD.6080005@quip.cz> References: <571F62AD.6080005@quip.cz>
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On Tue, Apr 26, 2016 at 7:44 AM, Miroslav Lachman <000.fbsd@quip.cz> wrote: > Hi, > > is there any way to make zpool scrub faster? > We have one older machine with CPU Pentium(R) Dual E2160 @1.80GHz, 5GB of > RAM and 4x 4TB HDDs. It is just a storage for backups for about 20 machines. > Scrub is scheduled from periodic each 30 days but it takes about 4 days to > complete and everything during scrub is slow. Backups takes 8 hours instead > of 5 (made by rsync), deleting of old files is even more slower. > > The backups are made every night from the midnight to morning, the machine > is idle for the rest of the day. > > Is there any tuning to make scrub faster in this idle time? > Or is it better to do it other way - slower scrub with even lower priority > taking for about one week but not affecting time of normal operations? (is > it dangerous to have scrub running this long or reboot machine during the > scrub?) It's likely easier to make scrub slower (but rsync faster) when the system is not idle, but hopefully no slower otherwise. I would start with increasing the vfs.zfs.scrub_delay (in ticks; typically 1/1000 of a second) settings to reduce scrub's impact to other IO this without impacting resilvers. (Expect longer total time as it will scrub less during rsyncs.) You can also increase vfs.zfs.scan_idle if scrub_delay isn't enough, but do note that vfs.zfs.scan_idle impacts resilvers, too -- so make sure you don't also increase vfs.zfs.resilver_delay, or you may get very slow resilvers during IO. The logic for this is in dsl_scan.c [1] -- look there for the final word on what the different parameters do; there are a number of informative comments throughout the file if you are not into the code itself. See also vfs.zfs.vdev.*_max_active and vfs.zfs.vdev.*_min_active, if you are really want more knobs to try. It's might also be worth trying '/usr/local/bin/perl /usr/share/dtrace/toolkit/hotkernel' to see what the kernel is up to... - Eric [1] https://svnweb.freebsd.org/base/releng/10.3/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c?view=markup or https://github.com/freebsd/freebsd/blob/releng/10.3/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
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