[OpenIndiana-discuss] Zfs stability "Scrubs"

Jim Klimov jimklimov at cos.ru
Tue Oct 16 00:24:44 UTC 2012

2012-10-16 3:57, Heinrich van Riel wrote:
> Understood, if full backups are executed weekly/monthly no scrub is
> required.

I'd argue that this is not a completely true statement.

It might hold for raidzN backing storage with single-copy blocks,
but if mirrors and/or two or three copies are involved (i.e. for
metadata blocks) or ditto blocks on deduped pools, you have say
a 50/50 or 33/67 chance of only reading once a particular copy
of a block during the backup'ing procedure, and if errors hide
in other copies - you'll miss them.

That's where scrub should shine, by enforcing reads of all copies
of all blocks while walking the block pointer tree of the pool.

Hope I'm correct ;)

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