April 21, 2008 (Computerworld) Western Digital Corp. today launched the first model of its new 2.5-in. VelociRaptor VR 150 hard-drive product line, which company executives said offers about twice the capacity of the 2.5-in. Raptor hard drive it will replace.

Some Specs:

• 300 GB
  


• 10,000 RPM
  


• SATA 3Gb/s interface
  


• 16MB Cache
  


• 1.4 million hours MTBF
  

Transfer Rates
Buffer To Host (Serial ATA) 3 Gb/s (Max)
Transfer Rate (Buffer To Disk) 120 MB/s (Sustained)

In keeping with our last post, we can see that this drive can "sustain" 120 MBPS (pretty good). But what is the IOPS for this drive? You will have to pull up the PDF on this drive to get additional information to calculate this value. If you do pull up the PDF, you will find:

• 5.5ms average latency
  


• 10,000 RPM
  


• 4.2/4.7ms Seek Time

Now to calculate IOPS:

Full Rotation is (1/ [RPM/60000] ) = 6ms

Rotational Latency is (Full Rotation)/2 = 3ms

Average Seek Time is (4.2+4.7)/2 = 4.45ms

IO Time is (Rotational Latency + Average Seek Time) = 7.45ms

IOPS is (1/IO Time)*1000 = 134 IOPS


I surely wouldn't be putting this drive in my SAN. This drive is being marketed for gaming and media type applications such as video editing which would be well served for the MBPS. This IOPS calculation is just always fun for me to do and then compare it to the "backend" interface, which is 3Gb/s here. You should get familiar with doing these calculations if possible. I am always surprised at the number of individuals that expect a drive to saturate the backend without ever understanding the application being used. I have even had architects tell me that they had a 4GB backend and therefore expected that transfer rate, even though they only had a handful of disks that could never generate that much traffic.