> 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.
As far as it's ability to withstand _any_ 2-disk failure... I'm not sure
what you mean by definition. RAID-6 implemations don't follow a standard
because there isn't one. Depending on how it's implemented, RAID-6 is not
necessarily able to withstand a filaure of any two disks. We can argue as
much as you want, but I'm not willing to invest the time.
> With a 1500MHz Athlon on a typical file server where there's not much
> writes, the CPU is sitting there chrunching RC5-64 som 99,95 % of the
> time. I don't think it'll make much differnce with today's CPUs
It's up to you to decide if the performance trade-off is worthwhile. I
merely trying to point out that system with 2 RAID-5 is likely to incur
the same CPU hit as a single RAID-6, implemented in the kernel.
--- Derek Vadala, derek@cynicism.com, http://www.cynicism.com/~derek- 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/