Richard Todd rmtodd at ichotolot.servalan.com
Tue Aug 12 04:04:49 UTC 2008

Jeremy Chadwick <koitsu at FreeBSD.org> writes:
> If Larry was using UFS, he'd also see the above errors from the kernel.
> FreeBSD reports the CRC errors reported by the ATA device, ZFS reports
> the said data as corrupted during scrubbing or standard usage (hence the
> CKSUM field in 'zpool status'), and ZFS also *repairs* the corrupted
> data.  I can't explain how the repair works, but it's one of the many
> features of the filesystem.  I believe journalling filesystems (e.g.

Um, not exactly.  It's one of the features of the filesystem when you're
running on a ZFS pool which is mirrored or raidz.   If your ZFS pool is
not mirrored or raidz-ed, checksum errors *will* be unrepairable and should
show up as read errors to the application.  AFAIK, the "repair" is just
ZFS either finding a good copy of the block from the other half of the 
mirror (if mirrored) or reconstructing the missing block thru parity (if
raidz-ed) and rewriting it. 

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