> can you guess? <billtodd <at> metrocast.net> writes: > > > > You really ought to read a post before responding > to it: the CERN study > > did encounter bad RAM (and my post mentioned that) > - but ZFS usually can't > > do a damn thing about bad RAM, because errors tend > to arise either > > before ZFS ever gets the data or after it has > already returned and checked > > it (and in both cases, ZFS will think that > everything's just fine). > > According to the memtest86 author, corruption most > often occurs at the moment > memory cells are written to, by causing bitflips in > adjacent cells. So when a > disk DMA data to RAM, and corruption occur when the > DMA operation writes to > the memory cells, and then ZFS verifies the checksum, > then it will detect the > corruption. > > Therefore ZFS is perfectly capable (and even likely) > to detect memory > corruption during simple read operations from a ZFS > pool. > > Of course there are other cases where neither ZFS nor > any other checksumming > filesystem is capable of detecting anything (e.g. the > sequence of events: data > is corrupted, checksummed, written to disk).
Indeed - the latter was the first of the two scenarios that I sketched out. But at least on the read end of things ZFS should have a good chance of catching errors due to marginal RAM. That must mean that most of the worrisome alpha-particle problems of yore have finally been put to rest (since they'd be similarly likely to trash data on the read side after ZFS had verified it). I think I remember reading that somewhere at some point, but I'd never gotten around to reading that far in the admirably-detailed documentation that accompanies memtest: thanks for enlightening me. - bill This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
