Re: RAID 1 or Hammer

[Michael Neumann <mneumann@xxxxxxxx>]

Am 12.01.2009 23:20, schrieb Simon 'corecode' Schubert:
> Konstantinos Pachnis wrote:
>>>> I'm curious if RAID 1 (mirroring) really helps to protect data loss.
>>>> Of course if a whole disk "dies", RAID 1 has the advantage that
>>>> I have an identical copy. But what happens if only a sector of one 
disk
>>>> contains bad data. How can the RAID controller decide which is the
>>>> correct sector? Or would the disk detect such a case and return an
>>>> error?
>>>>
>>
>> When the controller will try to perform an I/O operation it will fail
>> on the faulty disk (the disk with the bad sector). As a result the
>> controller will be able to decide which is the correct sector.
>
> You're assuming fail-stop errors. If it is a sneaking bit error or
> something else, it won't notice.

But Hammer won't notify this as well, right? IIRC, Hammer does CRC only
on meta-data.

Regards,

  Michael