On Wed, 3 Nov 2010, Warren Young wrote:
> To: CentOS mailing list <centos@xxxxxxxxxx>
> From: Warren Young <warren@xxxxxxxxxxx>
> Subject: Re: PATA Hard Drive woes
>
> On 11/3/2010 8:32 AM, Keith Roberts wrote:
>>
>> So to prepare the disk for returning under warranty, I used
>> another HDD utility to clean the disk again
>
> ...
>
>> So I ran an Advanced r/w scan again with Hitachi DFT, and
>> the result was OK.
>
> A complete disk wipe brings bad sectors to the drive's attention,
> forcing it to remap them using spare sectors set aside for the purpose.
>
> All drives can do this, and they do it without logging the change. You
> can't tell, from the outside, when or whether the drive has done this.
> All you can do is infer it, because a sector that once tested bad now
> tests good.
>
> As to why this happened only during a format, not during the previous
> disk test, it's probably because the format zeroed the disk. That
> particular drive may have a policy to only remap sectors on write, so as
> to preserve the sector contents for potential recovery later. (See
> below for one way this can be done.)
>
> It may be that your drive is now fine.
>
> If you put it back into service, at minimum I would set up smartd, from
> the smartmontools package. Maybe run smartctl on it by hand daily or
> weekly, too. If you find that errors start happening again, there is
> something continually degrading the drive's integrity, so the automatic
> sector remapping will eventually run the drive out of spare sectors.
>
> SpinRite (http://spinrite.com/) does nondestructive sector remapping.
> At level 4 and above, it reads each sector in and then writes it back
> out to the drive. Because remapping is silent, it's possible for it to
> appear to do nothing, yet improve data integrity by bringing dodgy
> sectors to the drive's attention.
>
> If a sector can't be read without error, SpinRite forces the drive to
> ignore the CRC and return the data anyway, retrying many times, then
> making a statistical guess about the most likely contents of the sector.
> (Reading a bad sector won't necessarily give the same value each try.)
> Then on writing the reconstructed data back out, the drive
> automatically remaps the sector, repairing it.
>
> You might want to combine the SMART monitoring with periodic SpinRite
> runs on the drive until you regain confidence in it.
Thanks Warren. I've read good reports about SpinRite.
I might shell out some dosh for a copy if it can
non-destructably repair bad sectors. I heard it's worth
running just to keep your HDD's in shape.
Regards,
Keith
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