Bad Blocks... Should I RMA?

Matthew Seaman m.seaman at
Mon Nov 16 06:56:15 UTC 2009

Lowell Gilbert wrote:
> "Ronald F. Guilmette" <rfg at> writes:
>> Nov 15 15:24:17 coredump kernel: ad4: FAILURE - READ_DMA status=51<READY,DSC,ERROR> error=40<UNCORRECTABLE> LBA=256230591
> This is *not* necessarily a big deal, despite what your other response
> told you.  Errors on reads do not mean that your drive's bad-sector
> table is full; only errors on write indicate that.  If you can try
> manufacturer's drive diagnostics, do that.  If you can't, then it's
> harder to fix things up, but not impossible; write back if you
> really can't use a low-level diag.

Yes -- this is correct.  It's possible for a disk to be unable to read a sector,
but rewriting the sector would either succeed and leave the sector fully working
again, or cause it to be remapped in which case the disk will subsequently perform 
perfectly well[*].

Beyond running the manufacturers diagnostics,  as the OP has said he has nothing particularly valuable on the drive, it might be worth running a few passes of dban
or similar on the disk --- this will overwrite every part of the platter and
should make it abundantly clear if there is a real and persistent problem.  If
you can't afford to scrub the disk, then just keep it under observation: if the
problems recur within a few weeks then yes, definitely RMA that drive.


[*] If the error messages have disappeared since, then this has probably
already happened.

Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP:     Ramsgate
                                                  Kent, CT11 9PW

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