On Mon, 3 Apr 2000, Bruce Sterling Woodcock wrote:
Strange, but I would think you could still get away with less disk per Netapp and just more Netapps and accomplish the same thing cheaper. But I guess EMC is giving you a good deal.
9GB drives are no longer available, 18GB drives will probably be EOL'd this year, and 36GB drives are the current standard. If the performance "sweet spot" is still 14 drives, that's ~400GB per filer. For my particular needs, storage is essentially infinite... NFS ops is what I crave. Give me a quad Alpha filer with two shelves of 15000 RPM 18GB Cheetahs, please. :)
I don't see how? When one mirror loses a disk, the whole thing is lost; you switch over to the other mirror, which has n-1 disks as the RAID 4 array. So your initial chance of failure is 2n-1 and then n-1 for a second failure whereas RAID 4 is just n followed by n-1 for the second failure.
I think you're talking about RAID 0+1 (taking a RAID-0 set and mirroring it on another RAID-0 set, which is just silly). RAID 1+0 does the mirroring first, then the striping/concatenation:
+----+----+ +--------------+ +------------+ | 1A | 1B | | RAID-1 set 1 | | | +----+----+ +--------------+ | | | 2A | 2B | | RAID-1 set 2 | | | +----+----+ +--------------+ | | | 3A | 3B | | RAID-1 set 3 | | | +----+----+ +--------------+ | | | 4A | 4B | --> | RAID-1 set 4 | --> | RAID 0 | +----+----+ +--------------+ |(7 "drives")| | 5A | 5B | | RAID-1 set 5 | | | +----+----+ +--------------+ | | | 6A | 6B | | RAID-1 set 6 | | | +----+----+ +--------------+ | | | 7A | 7B | | RAID-1 set 7 | | | +----+----+ +--------------+ +------------+ [etc...]
The A's and B's are drives of a mirrored pair. You could lose, say, drives 1A, 2A, 4B, 5B and 7A and still have a functional RAID 0, because no single mirror is completely broken. You could lose the entire shelf containing the A drives and not have an outage (something from which today's Netapps cannot automatically recover, clustering or no clustering). Having mirrored pairs in RAID 4 (i.e., having mirrored data and parity drives) and the ability to concurrently rebuild multiple broken mirrors to hot spares would really give Netapp a leg up on other NAS vendors, IMHO.
Oh, are the drives mirror images of each-other too? I didn't realize that. So if Drive 1 in Mirror A fails, breaking the mirror, and then Drive 2 in Mirror B fails, Mirror B will be smart enough to switch over to Drive 2 in Mirror A?
As far as the RAID 0 is concerned, single drive failures within each mirrored pair does not result in that stripe being down, because the remaining half of the mirror is still online. If you lose, say, drives 4A and 4B in a RAID 1+0, then you're toast. In RAID 1+4 (or 1+5), you would still have the parity drive.
Yes, I know about the support, but even so, is the support WORTH the extra you are paying for the hardware? What exactly is the price difference on what you evaluated?
We inherited a Symmetrix 3430 (using it as direct-attach SCSI, not NAS). It was not configured in the most intelligent manner to begin with, and it takes a lot of careful planning and detail work to ensure you didn't build yourself a rickety house of cards. I don't know how much the company paid for the EMC originally, but you also have to factor in the costs for the Veritas VxVM/VxFS licenses to efficiently manage all those disk targets. All this extra complexity not only makes outages more difficult to prevent, but usually means repair times go way up as well, as you try to remember all the intricacies of your whiz-bang RAID configuration. I'd rather just have Netapps humming away in the background, and trust in their magic. ;-)