Date: Wed, 09 May 2012 15:04:52 +0100 From: Johannes Totz <johannes@jo-t.de> To: freebsd-fs@freebsd.org Subject: Re: ZFS resilvering strangles IO Message-ID: <jodti4$dhv$1@dough.gmane.org> In-Reply-To: <4FAA14D6.8060302@brockmann-consult.de> References: <73F8D020-04F3-44B2-97D4-F08E3B253C32@grem.de> <4FAA14D6.8060302@brockmann-consult.de>
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On 09/05/2012 07:55, Peter Maloney wrote: > About the slow performance during resilver, > > Are they consumer disks? If so, one guess is you have a bad disk. Check > by looking at load and ms per x on disks. If one is high and others are > low, then it's probably bad. If a single 'good' disk is bad, the whole > thing will run very slow. Bad consumer disks run very slow trying over > and over to read the not-yet-bad sectors where enterprise disks would > throw errors and fail. > > My other guess is that this is because FreeBSD, unlike Linux and > Solaris, lacks IO scheduling. So there is no way for the zfs code to > truly put the resilver on lower priority than the regular production > applications. I've read that IO scheduling was developed for 8.2, but > never officially adopted. I would love to see it in FreeBSD... I use > "ionice" on Linux all the time (for copying, backups, zipping, > installing a a huge batch of packages [noticeable >300 MB], etc. while I > work on other things), so I miss it. IO scheduling on Solaris also helps > with dedup performance. > > Does anyone know if there is a movement to add the IO scheduling code > into the base system? There was a geom module for io scheduling: gsched(8) But I've never used it and don't know what the state of it is... > On 05/08/2012 04:33 PM, Michael Gmelin wrote: >> Hello, >> >> I know I'm not the first one to ask this, but I couldn't find a definitive answers in previous threads. >> >> I'm running a FreeBSD 9.0 RELEASE-p1 amd64 system, 8 x 1TB SATA2 drives (not SAS) and an LSI SAS 9211 controller in IT mode (HBAs, da0-da7). Zpool version 28, raidz2 container. Machine has 4GB of RAM, therefore ZFS prefetch is disabled. No manual tuning of ZFS options. Pool contains about 1TB of data right now (so about 25% full). In normal operations the pool shows excellent performance. Yesterday I had to replace a drive, so resilvering started. The resilver process took about 15 hours - which seems a little bit slow to me, but whatever - what really struck me was that during resilvering the pool performance got really bad. Read performance was acceptable, but write performance got down to 500kb/s (for almost all of the 15 hours). After resilvering finished, system performance returned > to normal. >> >> Fortunately this is a backup server and no full backups were scheduled, so no drama, but I really don't want to have to replace a drive in a database (or other high IO) server this way (I would have been forced to offline the drive somehow and migrate data to another server). >> >> So the question is, is there anything I can do to improve the situation? Is this because of memory constraints? Are there any other knobs to adjust? As far as I know zfs_resilver_delay can't be changed in FreeBSD yet. >> >> I have more drives around, so I could replace another one in the server, just to replicate the exact situation. >> >> Cheers, >> Michael >> >> Disk layout: >> >> daXp1128 boot >> daXp2 16G frebsd-swap >> daXp3 915G freebsd-zfs >> >> >> Zpool status during resilvering: >> >> [root@backup /tmp]# zpool status -v >> pool: tank >> state: DEGRADED >> status: One or more devices is currently being resilvered. The pool will >> continue to function, possibly in a degraded state. >> action: Wait for the resilver to complete. >> scan: resilver in progress since Mon May 7 20:18:34 2012 >> 249G scanned out of 908G at 18.2M/s, 10h17m to go >> 31.2G resilvered, 27.46% done >> config: >> >> NAME STATE READ WRITE CKSUM >> tank DEGRADED 0 0 0 >> raidz2-0 DEGRADED 0 0 0 >> replacing-0 REMOVED 0 0 0 >> 15364271088212071398 REMOVED 0 0 0 was >> /dev/da0p3/old >> da0p3 ONLINE 0 0 0 >> (resilvering) >> da1p3 ONLINE 0 0 0 >> da2p3 ONLINE 0 0 0 >> da3p3 ONLINE 0 0 0 >> da4p3 ONLINE 0 0 0 >> da5p3 ONLINE 0 0 0 >> da6p3 ONLINE 0 0 0 >> da7p3 ONLINE 0 0 0 >> >> errors: No known data errors >> >> Zpool status later in the process: >> root@backup /tmp]# zpool status >> pool: tank >> state: DEGRADED >> status: One or more devices is currently being resilvered. The pool will >> continue to function, possibly in a degraded state. >> action: Wait for the resilver to complete. >> scan: resilver in progress since Mon May 7 20:18:34 2012 >> 833G scanned out of 908G at 19.1M/s, 1h7m to go >> 104G resilvered, 91.70% done >> config: >> >> NAME STATE READ WRITE CKSUM >> tank DEGRADED 0 0 0 >> raidz2-0 DEGRADED 0 0 0 >> replacing-0 REMOVED 0 0 0 >> 15364271088212071398 REMOVED 0 0 0 was >> /dev/da0p3/old >> da0p3 ONLINE 0 0 0 >> (resilvering) >> da1p3 ONLINE 0 0 0 >> da2p3 ONLINE 0 0 0 >> da3p3 ONLINE 0 0 0 >> da4p3 ONLINE 0 0 0 >> da5p3 ONLINE 0 0 0 >> da6p3 ONLINE 0 0 0 >> da7p3 ONLINE 0 0 0 >> >> errors: No known data errors >> >> >> Zpool status after resilvering finished: >> root@backup /]# zpool status >> pool: tank >> state: ONLINE >> scan: resilvered 113G in 14h54m with 0 errors on Tue May 8 11:13:31 2012 >> config: >> >> NAME STATE READ WRITE CKSUM >> tank ONLINE 0 0 0 >> raidz2-0 ONLINE 0 0 0 >> da0p3 ONLINE 0 0 0 >> da1p3 ONLINE 0 0 0 >> da2p3 ONLINE 0 0 0 >> da3p3 ONLINE 0 0 0 >> da4p3 ONLINE 0 0 0 >> da5p3 ONLINE 0 0 0 >> da6p3 ONLINE 0 0 0 >> da7p3 ONLINE 0 0 0 >> >> errors: No known data errors >> >> _______________________________________________ >> freebsd-fs@freebsd.org mailing list >> http://lists.freebsd.org/mailman/listinfo/freebsd-fs >> To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org" > >
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