We measured throughput with two different tests. The MPC benchmark, which NSTL developed for the Multimedia PC Council in conjunction with Intel, measures data throughput for both random and sequential access. It determines how much CPU power disks need, and indicates what impact they will have on the delivery of multimedia content.
A second test, which uses the ThreadMark benchmark software from Adaptec (available at http://www.adaptec.com), is designed to indicate how well a disk subsystem handles periods of high I/O activity. We deem this test important because you're likely to find server applications where the drive handles a large number of requests from many different users. ThreadMark makes a series of measurements using a mixture of single and multithreaded requests across a range of request block sizes (2 KB to 64 KB).
Both the ThreadMark and the MPC benchmarks comprise our performance score, which equals from 65 to 80 percent of a drive's overall rating. Cost-per-gigabyte is another 5 to 20 percent of the overall score. Reliability, which is difficult to test, makes up the remaining 10 to 15 percent of the overall score. (See the article "Hard Drive Ratings".) We rated these hard drives by warranty length and by mean time between failures, or MTBF. (For the IBM drives, we assumed an average MTBF figure; see the print edition of the features table.) MTBF, measured in hours, is a calculated statistical attribut
e, determined by combining the MTBF numbers for all the components that make up the unit. A problem with relying on MTBF is that you can test it only with large numbers of identical samples. And even though storage densities are increasing, track widths are decreasing, making alignment, precision manufacturing, and head-motion control more critical than ever. Today's high-capacity drives are more reliable than ever thought possible, with 1 million hours MTBF being a common figure. Note that this is not the same thing as saying that a given drive will run without failing for 1 million hours; this figure actually translates to about a 99.999 percent uptime rate over one calendar year.
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Test Methodology
