Re: raid 5 crashed

[Wols Lists <antlists@youngman.org.uk>]

On 01/06/16 02:48, Brad Campbell wrote:
> Now, having said that :
> 
> Much better to try and get the array running in a read-only state with
> all disks in place and clone the data from the array rather than the
> disks after they've been ddrescued. In the case of a running array, a
> read error on one of the array members will see the RAID attempt to get
> the data from elsewhere (a reconstruction), whereas a read from a disc
> cloned with ddrescue will happily just report what was a faulty sector
> as a big pile of zeros, and *poof* your data is gone.
> 
> Set the timeouts appropriately (and conservatively) to give the disks
> time to actually report they can't read the sector. This will allow md
> to try and get it elsewhere rather than kicking the disc out because the
> storage stack timed it out as faulty.

Okay - so would this be better (a lot slower, possibly, but safe ...)

Use dd - so it DOES bomb on error! - and only replace the drive once
you've got a clean read off it. With 2TB drives, that should work so
long as they're not faulty. And if it's - JUST - a timeout issue,
this'll work fine?

Cheers,
Wol