On Apr 24, 2012, at 8:35 AM, Jim Klimov wrote: > On 2012-04-24 19:14, Tim Cook wrote: >> Personally unless the dataset is huge and you're using z3, I'd be >> scrubbing once a week. Even if it's z3, just do a window on Sunday's or >> something so that you at least make it through the whole dataset at >> least once a month.
It depends. There are cascading failure modes in your system that are not media related and cause bring your system to its knees. Scrubs and resilvers can trigger or exacerbate these. > +1 I guess > Among other considerations, if the scrub does find irrepairable errors, > you might have some recent-enough backups or other sources of the data, > so the situation won't be as fatal as when you look for errors once a > year ;) There is considerable evidence that scrubs propagate errors for some systems (no such evidence for ZFS systems). So it is not a good idea to have a blanket scrub policy with high frequency. > >> There's no reason NOT to scrub that I can think of other than the >> overhead - which shouldn't matter if you're doing it during off hours. > > "I heard a rumor" that HDDs can detect reading flaky sectors > (i.e. detect a bit-rot error and recover thanks to ECC), and > in this case they would automatically remap the revocered > sector. So reading the disks in (logical) locations where > your data is known to be may be a good thing to prolong its > available life. It is a SMART feature and the disks do it automatically for you. -- richard -- ZFS Performance and Training richard.ell...@richardelling.com +1-760-896-4422
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