Why does resilvering an entire disk, yield different amounts of data that was
resilvered each time.
I have read that ZFS only resilvers what it needs to, but in the case of
replacing an entire disk with another formatted clean disk, you would think the
amount of data would be the same each time a disk is replaced with an empty
formatted disk.
I''m getting different results when viewing the ''zpool
status'' info (below)
For example ( I have a two-way mirror with a small file on it )
Raidz pools behave the same.
bash-3.2# zpool replace zp c2t27d0 c2t28d0
bash-3.2# zpool status
pool: zp
state: ONLINE
scrub: resilver completed after 0h0m with 0 errors on Mon Oct 26 09:46:21 2009
config:
NAME STATE READ WRITE CKSUM
zp ONLINE 0 0 0
mirror ONLINE 0 0 0
c2t26d0 ONLINE 0 0 0
c2t28d0 ONLINE 0 0 0 [b] 73K resilvered[/b]
errors: No known data errors
bash-3.2#
bash-3.2# zpool replace zp c2t28d0 c2t29d0
bash-3.2# zpool status
pool: zp
state: ONLINE
scrub: resilver completed after 0h0m with 0 errors on Mon Oct 26 09:46:52 2009
config:
NAME STATE READ WRITE CKSUM
zp ONLINE 0 0 0
mirror ONLINE 0 0 0
c2t26d0 ONLINE 0 0 0
c2t29d0 ONLINE 0 0 0 [b]83.5K resilvered[/b]
errors: No known data errors
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This message posted from opensolaris.org
Bill Sommerfeld
2009-Oct-26 17:51 UTC
[zfs-discuss] Resilvering, amount of data on disk, etc.
On Mon, 2009-10-26 at 10:24 -0700, Brian wrote:> Why does resilvering an entire disk, yield different amounts of data that was resilvered each time. > I have read that ZFS only resilvers what it needs to, but in the case of replacing an entire disk with another formatted clean disk, you would think the amount of data would be the same each time a disk is replaced with an empty formatted disk. > I''m getting different results when viewing the ''zpool status'' info (below)replacing a disk adds an entry to the "zpool history" log, which requires allocating blocks, which will change what''s stored in the pool.
A Darren Dunham
2009-Oct-26 17:58 UTC
[zfs-discuss] Resilvering, amount of data on disk, etc.
On Mon, Oct 26, 2009 at 10:24:16AM -0700, Brian wrote:> Why does resilvering an entire disk, yield different amounts of data that was resilvered each time. > I have read that ZFS only resilvers what it needs to, but in the caseof replacing an entire disk with another formatted clean disk, you would think the amount of data would be the same each time a disk is replaced with an empty formatted disk. As long as the amount of data on the other side of the mirror is identical, you should be correct. In other words, it copies the in-use blocks over. It doesn''t copy every block on the disk.> I''m getting different results when viewing the ''zpool status'' info (below) > > > > For example ( I have a two-way mirror with a small file on it ) > Raidz pools behave the same. > > > bash-3.2# zpool replace zp c2t27d0 c2t28d0 > bash-3.2# zpool status > pool: zp > state: ONLINE > scrub: resilver completed after 0h0m with 0 errors on Mon Oct 26 09:46:21 2009 > config: > > NAME STATE READ WRITE CKSUM > zp ONLINE 0 0 0 > mirror ONLINE 0 0 0 > c2t26d0 ONLINE 0 0 0 > c2t28d0 ONLINE 0 0 0 [b] 73K resilvered[/b] > > errors: No known data errors > bash-3.2# > bash-3.2# zpool replace zp c2t28d0 c2t29d0 > bash-3.2# zpool status > pool: zp > state: ONLINE > scrub: resilver completed after 0h0m with 0 errors on Mon Oct 26 09:46:52 2009 > config: > > NAME STATE READ WRITE CKSUM > zp ONLINE 0 0 0 > mirror ONLINE 0 0 0 > c2t26d0 ONLINE 0 0 0 > c2t29d0 ONLINE 0 0 0 [b]83.5K resilvered[/b]The difference is only about 10K. That''s not much. The live filesystem is in flux on the disks as metadata trees are updated assuming you have any activity at all (even reads that might be causing inode timestamps to be rewritte). I wouldn''t consider this difference significant. -- Darren