June 18th, 2007 by eugene
Western Digital Caviar SE16 WD7500AAKS
The WD7500AAKS's basic specs are quite evolutionary. WD maintains the tried-and-true four-platter approach to achieve the drive's 750-gigabyte capacity. As has been the case with Caviar-style drives for years now, the firm specs the unit's average seek time at 8.9 milliseconds. Buffer size remains at 16 megabytes, standard for most of today's SATA units.
With this iteration, however, WD brings a couple new features to the table aimed at further refining reliability and power consumption. The first is an improved ramp load paradigm, a feature that parks the unit's read/write heads far away from delicate platters while the drive is powered off, ostensibly increasing non-operating shock resistance.
The WD7500AAKS's other newer feature is the company's "IntelliSeek" technology, a just-in-time approach that aims to minimize power draw. As we all know, today's hard drives feature rotating platters upon which hundreds of millions of individual sectors rest. In typical non-streaming use, data from a relatively small gathering of sectors is retrieved/written before the actuator then moves to the next group. Previous drives would maximize acceleration and deceleration of the actuator to get the read/write heads in place as quickly as possible.
Under the IntelliSeek paradigm, the drive moves the actuator just fast enough to get to the appropriate track as the target sector(s) approach the heads' location. This minimizes power draw with no hit to performance since the drive would have to wait until the appropriate data location rotated under the heads regardless of when the heads arrived in position. An analogy: consider an 11am hotel checkout and 1pm flight check-in. A traveler must leave the hotel by eleven and arrive by one, but can minimize the gasoline used by driving slowly... whether he gets to the gate by 11:30 or 12:59, he still boards the same flight and gets to his end destination at the same time.
In addition to contrasting the WD7500AAKS with all of today's leading 7200 RPM SATA drives, the following tests will also include WD's own 10K RPM Raptor. By virtue of its relatively limited capacity of 150 gigabytes, the drive's street price weighs in well under that of gargantuan 7200 RPM drives and thus merits inclusion in our charts:
|Hitachi Deskstar 7K1000 (1000 GB)||Current-generation competing unit|
|Maxtor MaXLine Pro (500 GB)||Previous-generation competing unit (mechanically identical to the DiamondMax 11)|
|Seagate Barracuda ES (750 GB)||Current-generation competing unit (mechanically identical to the Barracuda 7200.10)|
|Western Digital RE2 (500 GB)||Manufacturer's previous-generation unit (mechanically identical to the 500 GB Caviar SE16)|
|Western Digital Raptor WD1500ADFD (150 GB)||High-perfomance enterprise-/enthusiast- oriented 10K RPM SATA unit|
For 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.
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The WD7500AAKS clocks in with a measured average read access time of 13.7 milliseconds (ms), a figure quite similar to that of the 500-gigabyte WD5000YS. Subtracting 4.2 ms to account for a 7200 RPM spindle's rotational latency leaves the Caviar with a measured read seek time of 9.5 ms, 0.6 ms above WD's claim. Average write accesses come in at 15.0 ms, an improvement over WD's earlier offering.
WD's latest hits an impressive 97 MB/sec transfer rate in its outermost zone, improving upon the RE2 by a hefty 31% margin and even topping the 10K RPM Raptor by 10%. Rates decay down to 54.4 MB/sec by the time tests reach the innermost tracks, trailing the Raptor but nonetheless setting a 7200 RPM record.
It is important to remember that access 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!
StorageReview uses the following tests to assess non-server use:
StorageReview.com Office DriveMark 2006- A capture of VeriTest's Business Winstone 2004 suite. Applications include Microsoft's Office XP (Word, Excel, Access, Outlook, and Project), Internet Explorer 6.0, Symantec Antivirus 2002 and Winzip 9.0 executed in a lightly-multitasked manner.
StorageReview.com High-End DriveMark 2006- A capture of VeriTest's Multimedia Content Creation Winstone 2004 suite. Applications include Adobe Photoshop v7.01, Adobe Premiere v6.5, Macromedia Director MX v9.0, Macromedia Dreamweaver MX v6.1, Microsoft Windows Media Encoder 9.0, Newtek Lightwave 3D 7.5b, and Steinberg Wavelab 4.0f run in a lightly-multitasked manner.
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The SE16 delivers a StorageReview Office DriveMark of 877 IO/s per second (IOps). This figure represents a 15% increase over the WD RE2, though it trails Hitachi's terabyte Deskstar 7K100 by 5%.
In the High-End DriveMark, the WD7500AAKS distances itself even more from the WD5000YS, building upon the earlier drive with a substantial 23% improvement. The gap between the SE16 and the Deskstar also increases, however, with Hitachi's unit maintaining an 11% lead over WD's latest.
Three decidedly different entertainment titles cover gaming performance in StorageReview's test suite.
FarCry, a first-person shooter, remains infamous for its lengthy map loads when switching levels.
The Sims 2, though often referred to as a "people simulator," is in its heart a strategy game and spends considerable time accessing the disk when loading houses and lots.
Finally, World of Warcraft represents the testbed's role-playing entry; it issues disk accesses when switching continents/dungeons as well as when loading new textures into RAM on the fly.
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A small improvement over the RE2 leaves the SE16 at 746 IOps, lagging the Deskstar by 17% in our FarCry trace.
The WD7500AAKS musters 806 IOps/sec in our Sims 2 playback, a score that builds upon the RE2's by 17% but one that once again can not keep up with the category-leading Deskstar 7K1000.
When recreating World of Warcraft's disk access patterns, the SE16 weighs in at 633 IOps. This score again improves upon that of the RE2 and again manages to best all 7200 RPM drives save the Hitachi.
Unlike single-user machines (whether a desktop or workstation), servers undergo highly random, non-localized access. StorageReview simulates these multi-user loads using IOMeter. The IOMeter File Server pattern balances a majority of reads and minority of writes spanning requests of varying sizes.
IOMeter also facilitates user-configurable load levels by maintaining queue levels (outstanding I/Os) of a specified depth. Our tests start with the File Server pattern with a depth of 1 and double continuously until depth reaches 128 outstanding I/Os.
Drives with any sort of command queuing abilities will always be tested with such features enabled. Unlike single-user patterns, multi-user loads always benefit when requests are reordered for more efficient retrieval.
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When presented with a load that simulates the concurrent accesses one may find on multi-user servers, the WD7500AAKS performs quite similarly to the enterprise-oriented WD RE2. As queue depths exceed 16, the SE16 starts to trail the RE2 slightly. Even so, depths greater than 16 per spindle would (hopefully) not be often encountered. In the end, the WD7500AAKS maintains a tradition of leading multi-user performance that debuted with the firm's 400 GB RE2.
Noise and Power Measurements
Idle Noise- The sound pressure emitted from a drive measured at a distance of 3 millimeters. The close-field measurement allows for increased resolution between drive sound pressures and eliminates interactions from outside environmental noise. Note that while the measurement is an A-weighted decibel score that weighs frequencies in proportion to human ear sensitivity, a low score does not necessarily predict whether or not a drive will exhibit a high-pitch whine that some may find intrusive. Conversely, a high score does not necessarily indicate that the drive exhibits an intrusive noise profile.
Operating Power Dissipation- The power consumed by a drive, measured both while idle and when performing fully random seeks. In the relatively closed environment of a computer case, power dissipation correlates highly with drive temperature. The greater a drive's power draw, the more significant its effect on the chassis' internal temperature.
Startup (Peak) Power Dissipation- The maximum power dissipated by a drive upon initial spin-up. This figure is relevant when a system features a large number of drives. Though most controllers feature logic that can stagger the spin-up of individual drives, peak power dissipation may nonetheless be of concern in very large arrays or in cases where a staggered start is not feasible. Generally speaking, drives hit peak power draw at different times on the 5V and 12V rails. The 12V peak usually occurs in the midst of initial spin-up. The 5V rail, however, usually hits maximum upon actuator initialization.
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Nearly a year ago, we noted that the WD5000YS was among the quietest drives we had ever encountered when it came to both objective measurement and subjective listening. WD's latest continues that trend -- the SE16 turns in an impressively low idle-noise measurement of just 38.6 dB/A. That said, subjectively speaking, the 750 GB SE16 and 500 GB RE2 exhibit a similar noise characteristic- noticeable with concentrated attention but still a notch lower than all the competition. Seeks are just loud enough to be discerned over ambient noise.
At idle, the SE16 draws 8.3 watts, shaving a third of a watt off of the dissipation exhibited by the RE2. Such a score still doesn't match the enviable 7.9 watts delivered by Hitachi's Deskstar... even as the WD enjoys an advantage by incorporating four rather than 5 platters in its design. The WD7500AAKS does turn the tables when it comes to active power draw, however. Under a 100% access load, the SE16 hits a maximum of 10.6 watts while the Deskstar weighs in a full one-third higher at 14.2 watts. Interestingly, the older WD RE2 design manages to match the SE16's 10.2 watt score despite the latter's purported intelligent seek advantage.
In a notable contrast to the drive's sustained power dissipation under idle and active loads, the SE16 is the most power-hungry of drives when it comes to initial spinup from a cold start, drawing nearly 35 watts across both 12V and 5V rails.
The StorageReview.com Reliability Survey aims to amalgamate individual reader experiences with various hard disks into a comprehensive warehouse of information from which meaningful results may be extracted. A multiple-layer filter sifts through collected data, silently omitting questionable results or results from questionable participants. A proprietary analysis engine then processes the qualified dataset. SR presents results to readers through a percentile ranking system.
According to filtered and analyzed data collected from participating StorageReview.com readers, the Western Digital Caviar SE16 WD7500AAKS is more reliable than of the other drives in the survey that meet a certain minimum floor of participation.
According to filtered and analyzed data collected from participating StorageReview.com readers, a predecessor of the Western Digital Caviar SE16 WD7500AAKS, the Western Digital RE2 WD5000YS , is more reliable than of the other drives in the survey that meet a certain minimum floor of participation.
Note that the percentages in bold above may change as more information continues to be collected and analyzed. For more information, to input your experience with these and/or other drives, and to view comprehensive results, please visit the SR Drive Reliability Survey.
Though it comes close in our Office DriveMark suite, most of our single-user tests make it clear that the Caviar SE16 WD7500AAKS cannot go toe-to-toe with the monstrous Hitachi Deskstar 7K1000 when it comes to sheer performance. For those who value speed and capacity above all else, the 7K1000 remains king.
The WD7500AAKS nonetheless brings other advantages to the table, however. WD's latest performs quite well when contrasted with the other “huge drive” out there, Seagate's Barracuda 7200.10/ES. Further, the SE16's power draw and acoustic output are just about the lowest one can find from today's drives. Finally, at the time of this writing, scanning PriceGrabber's index of retailer pricing on the WD7500AAKS shows it enjoys a $40US or so advantage over the 750 GB version of the Deskstar 7K1000.
As a result, though it can not lay claim to the performance champion title, the SE16 may nonetheless merit a look when factors such as noise, heat, power, and price are thrown in. To many prospective buyers, WD's balance of all factors in its latest offering may be enticing.