[rescue] DiskSuite configuration suggestions

[George Adkins]

On Thursday 14 February 2002 03:48 am, you wrote:
> On Thu, Feb 14, 2002 at 02:58:39AM -0500, Patrick Giagnocavo wrote:
> > I don't have experience with DiskSuite but have always been partial to
> > RAID 10 or 0+1.  Each disk is mirrored by a second disk(level 1), then
> > striped (level 0) for speed.  Downside is that 4x18GB drives = 36GB of
> > space under such a scheme.
>
> Okay, how is this different from:
>
> stripe, containing two disks
> mirror the stripe
>
You stripe the mirrors in 0+1, because it allows you multiple failures.

If you stripe A,B,C,D and stripe 1,2,3,4 and mirror those stripes, the loss 
of any one of A,B,C,D AND the loss of any *one* of 1,2,3,4  and you lose the 
whole volume.

if you mirror  A1, B2, C3, D4 and then stripe those 4 mirrors, you can suffer 
4 independent failures, and so long as none of them include both drives of a 
mirrored pair, you still have your data.  Also, automatic mirror re-build is 
easier to accomplish under some hardware than non-parity stripe re-build.


Statistical analysis follows: based on 8 drives, in 0+1 and 1+0 arrangement
(based on my limited knowledge of ststistics)

mirrored stripe (1+0), loss of array with the failure of:
1 drive - 0%
2 drives ~ 57%
3 drives ~ 86%

striped mirror (0+1), loss of array with the failure of:
1 drive - 0%
2 drives ~ 14%
3 drives -~ 57%

George