WD fattens up S25 with third juicy platter
3G drive swells up to 900GB
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The third generation S25 drive from Western Digital has had a third platter added to reach the 900GB capacity point.
WD's S25 is a 2.5-inch enterprise disk drive spinning at 10,000rpm with a 6Gbit/s SAS interface. It comes in 150, 300 and 600GB capacity points and competes with Seagate's Savvio 10K – the 10K.4 600GB version of which has three 200GB platters compared to the second generation S25's 600GB with two platters.
However Seagate announced a 900GB Savvio 10K.5 in March last year, with 3 x 300GB platters using 506Gbit/in2 areal density, and a self-encrypting drive (SED) option. Then Hitachi GST went the 3-platter route with its Ultrastar C10K900 drive, with SED and the 6Gbit/s SAS interface. WD had to raise its game. There were two possible routes: move to 450GB or 500GB platters and produce a 900GB/1TB SV25 or go the added platter route.
It has chosen to add platters and the third generation SV25, with 300, 450, 600 and 900GB capacity points and 32MB cache, also has the SED option. Its transfer speed is 204MB/sec, compared to the second generation S25's 128MB/sec, and WD says it has a 2 million hour MTBF rating, an industry high.
Seagate's Savvio is unique among this 3-platter threesome in that it has a 4Gbit/s Fibre Channel interface as well as the SAS one. As Fibre Channel disk connectivity is thought to be on the way out, that is likely to remain a Seagate-only attribute.
With WD buying Hitachi GST and the acquisition being closed tomorrow, why has WD introduced a drive that competes with the Hitachi GST Ultrastar? It's surely partly because the Chinese competition regulators require Hitachi GST to operate independently of WD for two years, which includes separate research and development activities, and so we will have the ludicrous situation of a parent competing with its own arms-length subsidiary.
This S25 move sparks off thoughts of a 900GB Velociraptor, since Velociraptor is a10K, 2.5-inch drive with 150GB to 600GB capacity points and two platters. Its users would sure appreciate the added data velocity a third platter would give them. ®
COMMENTS
Re: fuzzy math?
that's correct: "enterprise" disks only ever use quite narrow bands of the outer part of the disk, since that gives the lowest latency. these disks are sold on iops, not bandwidth. (which is why, more than ever, they sell to a shrinking niche market. think SSD...)
Unless ...?
Unless, of course, the industry definition of areal density is simply the number of bits stored on a platter divided by (pi times radius squared). It doesn't necessarily make sense to exclude the hole in the middle, since its necessary size may be part of a complex design trade-off. Thinks ... a smaller hole means a narrower spindle which will be less rigid and vibrate more, meaning you have to put the tracks further apart to allow for that. So there's definitely an optimum to be sought.
Reliabilty?
Well, I hope they're a bit more reliable than the external 640 gig "Elements" drive of theirs I bought a few years back. After about a year, the interface electronics failed, although the drive itself itself was OK at the time, as proved by installing it in a spare external housing. That lasted about another six months before failing. They don't seem to have a particularly good reputation for longevity. Not impressed. Wouldn't buy another!
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