"Karl" == Karl Swartz kls@netapp.com writes:
>> True, these numbers don't translate directly into availability, >> since you now have almost twice as many drives to worry about, >> compared to a RAID 4 of similar capacity. Still, this is better than >> the 100% chance of a RAID 4 dying with 2 or more broken disks.
Karl> It's a somewhat minor nit, but I feel obliged to point out Karl> that while NetApp uses RAID 4, and a RAID 4 set will croak Karl> if it suffers a double disk failure, it's not necessarily Karl> true that a double disk failure will take out a filer. A Karl> sufficiently large volume on a filer will be RAID 4+0 (I Karl> think I got the notation right -- it's a concatenation of Karl> several RAID 4 group), and you can have multiple volumes.
Actually, concatenation is not defined as one of the raid levels. RAID 0 is striping. So if the NetApp were striping a volume across the RAID 4 groups, then it would be RAID 4+0 (or RAID 0+4). And if you striped multiple volumes across multiple RAID 4 groups, then you'd have something like EMC's RAID-S with Hypervolumes, except using RAID 4 instead of RAID 5. Phew, I believe this thread has now come full-circle and may safely die.
j.