Down to details
Although the VelociRaptor's novel design is easily the drive's defining feature, a 10,000 RPM spindle speed is what makes it a Raptor. Western Digital is still the only hard drive maker offering 10K-RPM drives with Serial ATA interfaces, which may be part of the reason why the Raptor is updated so infrequently. The other reason, WD tells us, is because once enterprise versions of the Raptor are qualified by server vendors for use in their systems, they'd rather keep using the same drive rather than have to re-qualify new versions on a regular basis.
|Raptor EL150||Raptor VR150|
|Maximum external transfer rate||150MB/s||300MB/s|
|Sustained data rate||88MB/s||120MB/s|
|Average read seek time||4.7ms||4.2ms|
|Average write seek time||5.9ms||4.7ms|
|Spindle speed||10,000 RPM||10,000 RPM|
|Available capacities||36GB, 74GB, 150GB||300GB|
|Idle acoustics||29 dBA||29 dBA|
|Seek acoustics||36 dBA||36 dBA|
|Mean Time Between Failures (MTBF)||1.2 million hours||1.2 million hours|
|Warranty length||Five years||Five years|
High spindle speeds have always allowed Raptors to offer incredibly low seek times, and the VelociRaptor is the fastest example yet. The drive's read seek time is half a millisecond quicker than WD's existing 3.5" Raptor, and its write seek time is a whopping 1.2 milliseconds faster. Milliseconds might not sound like much in the real world, but within the confines of a modern PC where bits are flipping at billions of times per second on multiple processor cores, there's not a moment to spare.
So why does the VelociRaptor seek quicker than its predecessor if both share the same 10K-RPM spindle speed? Partially because the VelociRaptor's smaller platters are easier for the drive head to traverse, as we discussed above. The VelociRaptor also packs a much higher areal density than its 3.5" forebear, giving the drive head access to more data over shorter physical distances. While existing Raptors only squeeze 74GB onto their 3.5" platters, the VelociRaptor's much smaller 2.5" platters pack 150GB each.Another dynamic we discussed above comes into play here, as well. The VelociRaptor's 2.5" platters have a much smaller outer edge circumference, somewhat offsetting the impact of its increased areal density on sequential transfer rates. Mind you, the VelociRaptor's sustained data rate is still 36% higher than the prior Raptor, with a faster 300MB/s Serial ATA interface to back it up.
The VelociRaptor needs only two platters to reach its 300GB capacity. Western Digital says it's also working on a single-platter version of the drive, but that's not ready yet.The VelociRaptor is clearly Western Digital's flagship performance drive, and at $300 for 300GB, it's not a cheap proposition. You'd think for such a premium product, Western Digital would have made every attempt to keep up with the Joneses. But the VelociRaptor only has 16MB of cache and that's, well, less than the 32MB cache on many terabyte drives. Western Digital says it did extensive performance profiling to evaluate larger cache sizes, but that it found little performance benefit in jumping up to 32MB. I can't say that we've ever found evidence to the contrary in our own testing, but given the VelociRaptor's competition and the drive's premium status, it's hard to understand why WD didn't go with a 32MB cache to hedge its bets.
At least Western Digital has preserved the Raptor's five-year warranty—an attribute that comes from its enterprise roots. Western Digital's standard desktop drives are only covered by a three-year warranty, although it is worth noting that Seagate offers five years of warranty coverage on all its internal hard drive products, including standard desktop models.
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