On Fri, 6 Apr 2012, James Harper <james.harper@bendigoit.com.au> wrote:
and even then, IMO, you'd be better off using, say, 240GB SSDs rather than 300GB SAS drives - 20% less storage but many times the IOPS, for roughly the same price. even 500-ish GB SSDs aren't that much more than 600GB 15k SAS disks, about $860 for a 480GB Intel 520 vs about $575 for an IBM 15k 600GB SAS....80,000 IOPS vs what, maybe 1000?
According to the HP Configureaider:
300GB 2.5" 10KRPM SAS - $422 300GB 2.5" 15KRPM SAS - $772 200GB 2.5" MLC SSD SAS - $4696
I'd be careful about sticking your $860 SSD into a server if you require any sort of write performance or durability, you might find you get just what you paid for.
Even if the $4696 SSD doesn't happen to be better than the $960 SSD, there's the issue that many companies want to buy everything from the same place. Sometimes if HP (or whoever the preferred provider is) doesn't sell it then it's not going in the server and we just have to work with that.
OTOH, if your workload is read-only (or read-mostly), a cheap(er) SSD may be well worth the investment vs 15KRPM disks.
(*) a large part of the point of RAID is that it is a Redundant Array of *Inexpensive* Disks. enterprise drives fail on that particular point. the disks are meant to be cheap and replacable commodity parts.
... or Redundant Array of *Independent* Disks, as if the name tells you what sort of disks you should be using anyway.
http://www.cs.cmu.edu/~garth/RAIDpaper/Patterson88.pdf The original paper on RAID says that the I stands for "Inexpensive" and contrasts it to "Single Large Expensive Disks (SLED)".
At 15KRPM you can read a single track in half the time, and therefore twice the speed.
You can read a track in half the time and on average read one sector in half the time once the heads are on the correct track. The head movement time won't be changed due to a different rotational speed. However the SCSI/SAS disks have bigger magnets for moving the heads (open some drives and inspect them) so the head movement time is probably lower in such disks. I will have to bring some dead disks to a LUV meeting so interested people can look inside them. Would anyone be interested in this before the next meeting?
You would also get additional gyroscopic stability although I don't know if that makes a difference in reality...
Such additional gyroscope action would mean more forces on the spindle and more possibility for things to wear out.
someone (on LUV I think) mentioned that consumer grade disks performance suffered much more when placed in an environment with vibration (eg adjacent to other seeking disks in a server).
The only case I'm directly aware of where disks suffered badly in production from this concerned enterprise grade disks, and the cause was vibration from system cooling fans - other systems of the same make and model didn't cause the same performance problems due to manufacturing differences in the fans. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/