zfs discuss - Jul 2009 - Ditto blocks on RAID-Z pool.

Hello all,

If you have copies=2 on a large enough raid-z(2) pool and 2(3) disks
die, is it possible to recover that information despite the offline
state of the pool?

I don''t have this happening to me, it''s just a theoretical
question.
So, if you can''t recover the data, is there any advantage to using
ditto
blocks on top of raid-z(2)?

Jebnor

-- 
Louis-Fr?d?ric Feuillette <jebnor at gmail.com>

Louis-Fr?d?ric Feuillette wrote:
> Hello all,
>
> If you have copies=2 on a large enough raid-z(2) pool and 2(3) disks
> die, is it possible to recover that information despite the offline
> state of the pool?
>
> I don''t have this happening to me, it''s just a
theoretical question.
> So, if you can''t recover the data, is there any advantage to using
ditto
> blocks on top of raid-z(2)?
>   
Yes, there is an advantage.  But it is not for the case where the whole
disk completely fails.  The advantage of copies is when the data cannot
be read, which is occurs more often than whole disk failure.
 -- richard