> > > It'll waste 9 drives, giving me a total capacity of 7n instead of 14n.
> > > And, by definition, RAID-6 _can_ withstand _any_ two-drive failure.
> >
> > This is certainly not true.
> >
> > Combining N RAID-5 into a stripe wastes on N disks.
> >
> > If you combine two it wastes 2 disks, etc.
> >
> > That is, for each RAID-5 you waste a single disk worth of storage for
> > partiy. I don't know what equation you're using where you get 9 drives
> > from.
>
> He was thinking "mirror", not "stripe". Mirror of 2 RAID-5 arrays (would
> be probably called RAID-15 (when there is a RAID-10 for mirrored stripe
> arrays)), can withstand any two disks failing anytime. Even more for
RAID-1 over two RAID-5s should withstand any three failures, AFAICS.
You could do RAID-5 over RAID-5. That should survive any 2 failures and
still be reasonably efficient.
Pavel
-- Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt, details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/