On Mar 10, 2017, at 9:28 AM, Valeri Galtsev <galtsev at kicp.uchicago.edu> wrote: > > > On Fri, March 10, 2017 9:52 am, Warren Young wrote: >> On Mar 10, 2017, at 6:32 AM, James B. Byrne <byrnejb at harte-lyne.ca> wrote: >>> >>> On Thu, March 9, 2017 09:46, John Hodrien wrote: >>>> >>>> fsck's not good at finding disk errors, it finds filesystem errors. >>> >>> If not fsck then what? >> >> badblocks(8). > > And I definitely will unmount relevant filesystem(s) before using > badblocks… You don’t necessarily have to. The default mode of badblocks is a non-invasive read-only test which is safe to run on a mounted filesystem. That said, a read-only badblocks pass can give a false “no errors” report in cases where a non-destructive read-then-write pass (-n) will show errors. Alternatively, a read-only pass may show an error that a read-then-write pass will silently bury by forcing the drive to relocate the bad sector. In extreme cases, you could potentially fix a problem with a read-random-random-write pass (-n -t random -t random) because that will statistically flip all the bits at least twice, which may rub the drive’s nose in a bad sector, forcing a reallocation where a normal read-then-write pass (-n alone) may not. Hard drives are weird. It is only through the grace of ECC and such that they approximate deterministic behavior as well as they do.