Date: Thu, 22 Apr 2010 17:11:06 +0200 From: Adam Nowacki <nowak@xpam.de> Cc: freebsd-fs@freebsd.org Subject: Re: zfs: unexpected resilver of old disk when attaching a new mirror disk Message-ID: <4BD0670A.8070205@xpam.de> In-Reply-To: <201004221441.PAA07296@wratting.cam.lispworks.com> References: <201004221441.PAA07296@wratting.cam.lispworks.com>
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My best guess is metadata updates to refer to the 2nd disk. I've seen same behavior when replacing a bad disk in 10 disk raidz2 pool. No data was affected. Martin Simmons wrote: > When I attach a second disk to a single-disk zpool to make a mirrored pool, > the original disk is partially resilvered. Is that expected? It makes me > worry that some of the good data is being overwritten. > > It happens on 8.0-RELEASE (pool version 13) and the 9.0-CURRENT-201004 > snapshot (pool version 14). It doesn't happen on Open Solaris snv_111b (also > pool version 14). > > My setup commands for the test, making a 64MB zpool containing a 16MB file > are: > > dd if=/dev/zero of=/tmp/zdisk0 bs=1m count=64 > zpool create ztest /tmp/zdisk0 > dd if=/dev/zero of=/ztest/a-file bs=1m count=16 > > The pool looks as expected: > > pool: ztest > state: ONLINE > scrub: none requested > config: > > NAME STATE READ WRITE CKSUM > ztest ONLINE 0 0 0 > /tmp/zdisk0 ONLINE 0 0 0 > > errors: No known data errors > > I then attach a second device: > > dd if=/dev/zero of=/tmp/zdisk1 bs=1m count=64 > zpool attach ztest /tmp/zdisk0 /tmp/zdisk1 > > and the pool looks like this after a while: > > pool: ztest > state: ONLINE > scrub: resilver completed after 0h0m with 0 errors on Thu Apr 22 00:29:32 2010 > config: > > NAME STATE READ WRITE CKSUM > ztest ONLINE 0 0 0 > mirror ONLINE 0 0 0 > /tmp/zdisk0 ONLINE 0 0 0 86K resilvered > /tmp/zdisk1 ONLINE 0 0 0 16.1M resilvered > > errors: No known data errors > > As expected, /tmp/zdisk1 was resilvered with 16MB of data for /ztest/a-file, > but why was a small amount of /tmp/zdisk0 also resilvered? > > The amount varies varies (I've seen up to 220K) but it is never 0. With real > disks constaining 5GB, the amount resilvered on the old disk is up to 70MB and > it increases gradually from 0 as the resilvering of the new disk proceeds. > > __Martin > _______________________________________________ > 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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