On Sun, 18 Jul 2021 at 00:30, Greg Troxel <g...@lexort.com> wrote: > > [snip] > > Ah, interesting point. I find this confusing, because I thought an > uncorrectable read error would, for disks I've dealt with, cause the > sector to be marked as permanently failed and pending reallocation. > It depends where the failure occurs I expect. A drive could read just fine, but then a damaged cable may cause enough noise that the data doesn't always make it to the controller correctly.
> I also didn't realize that wd(4) would issue aother read when there is a > failure, but maybe that's in zfs glue code. > wd has retried for years I think, it certanly used to do that with the soft RAID code. Looks to be set at 5 in the source[1], if I'm looking in the right place. :D I expect if you just use wd devices for ZFS there may be some merit in setting the retries to 1 and letting ZFS deal with it, it'd stop the slow I/O, with the effect of ZFS failing the drive. [snip] > >> 5 200 140 yes online positive Reallocated sector count 0 > > > > I was expecting to see this value greater than 0 if the drive was > > failing, is the drive bad or the cabling? > > Sectors get marked as failed, and then they actually get reallocated > when you write. > I bet after a dd of /dev/zero that will go up. This is useful to know!. :) Ian 1. https://github.com/NetBSD/src/blob/05082e19134c05f2f4b6eca73223cdc6b5ab09bf/sys/dev/ata/wd.c#L94
