On 20/02/2013 09:01, Reindl Harald wrote:
Am 20.02.2013 00:52, schrieb Gordan Bobic:
> On 02/19/2013 10:00 PM, Reindl Harald wrote:
>> data without a raid are useless
>
> My point was that even RAID is next to useless because it doesn't protect you
against bit-rot.
it does
OK, say you have RAID1. One of the disks has a rotted sector. Your RAID
implementation can detect that the mirrors don't match but there's no
way to tell which is correct without an additional checksum.
Similar for RAID5 - you can detect that the data doesn't match the
checksum, but you have no way of being able to tell which n out of n+1
blocks are correct.
>> and in case of
>> RAID you have to have at least one full backup
>> and so it does not care me if disks are dying
>
> Depends how many versioned backups you have, I suppose. It is possible to not notice
RAID silenced bit-rot for a
> long time, especially with a lot of data
what do you think why a weakly raid-check is running
per default and any high-grade RAID does srub?
My point is that there isn't enough data in n+1 (RAID[1|5]) to work out
which set of blocks is correct to rebuild the data from. With RAID6 you
can do this, but not with lower levels of RAID.