Bill Broadley wrote:
The differences I've seen between "raid edition" drives and regular drives are:
Thanks for the thoughtful comments. I don't claim to be an expert in any of this. I just hope I'm asking the right questions.
* Dramatically better vibration resistance. If you are going to bolt a drive or two into a desktop it doesn't matter so much. If you are going to plug a drive into a 16 bay enclosure or even into a 1U node with a ton of fast fans you might well see a large performance difference because of the vibration. The specification sheets do reflect this btw, I assume this is mostly lower density platters and stronger motors for positioning the heads. This is especially noticeable on the consumer drives with the higher density platters (375-500GB per platters). I've seen consumer drives that manage 120MB/sec drop to a noisy fluctuation between 18-30 MB/sec because of vibration
Wouldn't the effect of vibrations from multiple drives depend greatly on the mechanical properties of the bay enclosure and the chassis itself? For example, I have a 16 bay enclosure that's built like a tank (I know because I dropped it once). I would think that the vibration of one drive would barely be noticed by others. Of course this question could be answered by measuring, assuming the presence of the right instrumentation, which I don't have.
* Consumer drives (at least the non-media ones) often have occasional thermal recalibrations. This seems better these days, but last thing you want is a recal triggering a degraded array.
What does the RAID controller and OS see when such a thing happens?
* Consumer drives will go to heroic efforts to read a bad sector, exactly the opposite of what you want in a RAID drive. In a RAID it's better to fail and yell bloody murder... especially when the rereading a sector a bunch causes the raid to time out and drop the disk.
But wouldn't failing and yelling bloody murder be treated by the RAID controller the same as when a drive times out? In either case, I would expect the RAID controller to see the drive as having failed. Then, when you replace the drive you'd cause a RAID unit rebuild which is a very dangerous thing to do these days given how large drives are and the chances of an I/O error occurring during the rebuild.
Of course manufactures claim various things about error rates per billion bits, designed duty cycles (40 hours a week vs 24/7), improve temperature envelops, and related. Alas while this is nice to hear I've not seen any direct results because of it.
I too agree it would be nice but neither you nor Google appear to be seeing it (assuming, as one poster said, that we're all using the same definition of "enterprise drive"). What's surprising to me is that if this were true then I'd expect the manufacturer's warranty to be different for the two classes of drives. Maybe this is the reason that Seagate is changing to a 3-year warranty for their consumer drive (I haven't seen anything about the warranty for the enterprise drives).
As an example, 500GB wd caviar $64.99, 500GB WD RE3 $89.99. IMO if you are building a raid or heavily used 1U with a ton of fans the extra $25 is worth it.
If there are real differences between the drives then this would be an easier decision. There doesn't appear to be a consensus, however, that the differences in the field are significant. Cordially, -- Jon Forrest Research Computing Support College of Chemistry 173 Tan Hall University of California Berkeley Berkeley, CA 94720-1460 510-643-1032 jlforr...@berkeley.edu _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
