> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Jim Klimov > > Logically, yes - I agree this is what we expect to be done. > However, at least with the normal ZFS reading pipeline, reads > of redundant copies and parities only kick in if the first > read variant of the block had errors (HW IO errors, checksum > mismatch).
I haven't read or written the code myself personally, so I'm not authoritative. But I certainly know I've heard it said on this list before, that when you read a mirror, it only reads one side (as you said) unless there's an error; this allows a mirror to read 2x faster than a single disk (which I confirm by benchmarking.) However, a scrub reads both sides, all redundant copies of the data. I'm personally comfortably confident assuming this is true also for reading the redundant copies of raidzN data. _______________________________________________ zfs-discuss mailing list firstname.lastname@example.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss