Faceoff at One Terabyte: Seagate's Barracuda ES.2 and WD's Caviar GreenPower
Access Time and Transfer RateFor diagnostic purposes only, StorageReview measures the following low-level parameters: Average Read Access Time- An average of 25,000 random read accesses of a single sector each conducted through IPEAK SPT's AnalyzeDisk suite. The high sample size permits a much more accurate reading than most typical benchmarks deliver and provides an excellent figure with which one may contrast the claimed access time (claimed seek time + the drive spindle speed's average rotational latency) provided by manufacturers. Average Write Access Time- An average of 25,000 random write accesses of a single sector each conducted through IPEAK SPT's AnalyzeDisk suite. The high sample size permits a much more accurate reading than most typical benchmarks deliver. Due to differences in read and write head technology, seeks involving writes generally take more time than read accesses. |
WB99 Disk/Read Transfer Rate - Begin- The sequential transfer rate attained by the outermost zones in the hard disk. The figure typically represents the highest sustained transfer rate a drive delivers.
WB99 Disk/Read Transfer Rate - End- The sequential transfer rate attained by the innermost zones in the hard disk. The figure typically represents the lowest sustained transfer rate a drive delivers.
For more information, please click here.
The Barracuda ES.2 weighs in with a 12.7 millisecond (ms) seek time, about a half-millisecond above the drive's predecessor. Accounting for the drive's 7200 RPM spindle speed (4.2 ms latency) leaves the unit with a measured access time of 8.5 ms... bravo Seagate, right on the money. The ES.2 joins the ES 750 now as the second consecutive Seagate offering that meets the firm's claimed specs... a welcome turnaround from a company that used to publish overly optimistic claims that often were missed by its ATA/SATA drives.
We have to take a different approach when assessing the Caviar GP's seek time since WD does not explicitly give users the drive's spindle speed. The GP turns in a measured access time of 15.0 ms, a score that lags the 7200-RPM WD7500AAKS by a significant margin. The WD7500AAKS's measured seek time when accounting for 4.2 ms of 7200 RPM latency is 9.5 ms (missing the firm's claim by over half a millisecond). Assuming the GP also shares such a seek time, that leaves us with 15 ms [measured access time] minus 9.5 ms [assumed seek time] which equals 5.5 ms, almost exactly the rotational latency associated with a 5400 RPM spindle speed.
Seagate's latest is the first SATA drive to bust through the 100 MB/sec plateau through achieving 104 MB/sec of transfer in its outermost zones. Rates decay down to a more pedestrian 53.3 MB/sec.
The Caviar GP's outer-zone score clocks in at 79.8 MB/sec and as a result lags the older, less dense WD7500AAKS by 21%. Assuming similar sector-per-track zone configurations, a 7200 RPM drive would boast a 33% advantage over a 5400 RPM unit. The difference between the GP and the WD7500AAKS is less than that, likely of course due to a density advantage on the GP's part. Nevertheless, this second low-level diagnostic again suggests a 5400 RPM spindle speed.
First half of the Barracuda ES.2's Transfer Rate Graph
Second half of the Barracuda ES.2's Transfer Rate Graph
|
Some Perspective It is important to remember that seek time and transfer rate measurements are mostly diagnostic in nature and not really measurements of "performance" per se. Assessing these two specs is quite similar to running a processor "benchmark" that confirms "yes, this processor really runs at 2.4 GHz and really does feature a 400 MHz FSB." Many additional factors combine to yield aggregate high-level hard disk performance above and beyond these two easily measured yet largely irrelevant metrics. In the end, drives, like all other PC components, should be evaluated via application-level performance. Over the next few pages, this is exactly what we will do. Read on! |