Re: emergency call for help: raid5 fallen apart

[John Robinson <john.robinson@anonymous.org.uk>]

On 25/02/2010 17:41, Dawning Sky wrote:
> On Thu, Feb 25, 2010 at 8:45 AM, John Robinson
> <john.robinson@anonymous.org.uk> wrote:
>> On 25/02/2010 08:05, Giovanni Tessore wrote:
>> [...]
>> I do think we urgently need the hot reconstruction/recovery feature, so
>> failing drives can be recovered to fresh drives with two sources of data,
>> i.e. both the failing drive and the remaining drives in the array, giving us
>> two chances of recovering every sector.
> 
> I was one of those 4 cases in the part month.  I would have certainly
> benefited from this when I tried to replace a failing drive on my old
> raid-5.  But  I think actually the redundancy you desired can be
> achieved by running a raid-6 at the degraded mode (with 1 missing
> drive).
> 
> Do I miss something?  If this is the case, shouldn't we all
> be doing this instead of using the raid-5?

I think you must be missing something, yes. RAID-6 with one drive 
missing would have 2 chances of recovering each sector, but then so does 
RAID-5 with no drives missing. In either case, lose a drive and you need 
every sector on the remaining drives to be good to complete the 
reconstruction and keep the array up.

Cheers,

John.