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IBM Ultrastar 36Z15
  June 20, 2001 Author: Eugene Ra  

IBM Ultrastar 36Z15 Available Capacities *
Model Number
18.3 GB
36.7 GB
* The benchmark scores presented in this review represent expected performance across the entire line.
Estimated Flagship Price: Not available at time of press (36.7 GB)
Evaluation unit provided by IBM Corp.


Technology watchers around the world cheered late February 2000 when Seagate announced the long rumored Cheetah X15, the world's first drive to reach a spindle speed of 15,000 rotations per minute. The X15's low access times allowed the drive to shatter performance records. Seagate enjoys a reputation of being first to hit new spindle speeds- 15k RPM was no exception. The X15 stood alone for more than a year as the sole offering representing a higher level of performance. Seagate's monopoly always ends, however... as the new technology matures, competitors roll out their designs.

As usual, Big Blue is the first to join Seagate at a higher spindle speed, this time with its Ultrastar 36Z15. Thankfully, unlike its previous first-generation unit at 10k RPM, IBM's new offering comes in a low profile, 1" high form factor. The 36Z15 flagship features 6 platters each storing 6.1 gigabytes of data... a net capacity of 36.7 GB. This assembly features a 4.2 millisecond seek time. An 18 GB model will also be available. Rather than utilizing the three platters that one would expect, the smaller unit uses four. Through distribution of 18 gigabytes of data across four six-gig platters, the smaller 36Z15 shaves specified seek times down to 3.4 milliseconds. Both drives come equipped with a four-megabyte buffer.

In this review we'll take a look at the flagship 36.7 gig unit. We hope to examine the 18 GB model in the near future. When reviewing SCSI drives, we usually stick to 68-pin LVD models. At the time of testing, however, IBM could only offer us an 80-pin SCA unit along with an adapter to convert the drive down to standard 68-pin data and 4-pin Molex power connections. To expedite results, we accepted the SCA drive. The results presented below also represent the 68-pin LVD unit.

As a drive meant to take on the Cheetah X15. the Ultrastar 36Z15 aims squarely at enterprise-level server and high-end workstation markets where speed is the utmost of concerns. Its 36-gig capacity, double that of Seagate's first-generation X15, allows deployment in capacious applications that previously had to stick to 10k RPM offerings. IBM backs the drive with a 5-year warranty.

Let's see how the 36Z15 stacks up in low-level tests!

WB99/Win2k Low-Level Measurements

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Click here to examine the STR graph for this drive

The principal advantage of higher spindle speeds is not higher transfer rates but instead lower rotational latencies and thus reduced access times. An increase from 10k RPM to 15k RPM operation yields a reduction in average rotational latency from 3.0 milliseconds to 2.0 milliseconds. This 1 ms reduction is more significant than it appears... after all, it's applicable in -all- seek situations, whether it be a 20 millisecond full-stroke or a sub-one millisecond track switch.

According to WinBench 99, the Ultrastar 36Z15's measured access time clocks in at 6.7 milliseconds. When taking the 2.0 ms of average rotational latency into account (access time = seek time + latency), the drive's measured seek time weighs in at 4.7 milliseconds, a bit off of its claimed 4.2 ms. Even so, such a figure is low enough to undercut the Seagate Cheetah X15 by a hair... a margin of just 0.1 ms.

The 36Z15's increased areal density allows it to sustain transfers higher than that of the X15, though not by as large a margin as many may expect. The drive's score of 49.1 MB/sec bests the X15 by about 20%. A current-generation 10k RPM drive like Seagate's Cheetah 73LP, however, outraces the 36Z15 by a significant margin.

WB99/Win2k WinMarks

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The Ultrastar 36Z15's score of 10.0 MB/sec in the Business Disk WinMark and 25.4 MB/sec in the High-End Disk WinMark shatter records set not too long ago by Seagate's Cheetah 73LP. This, of course, means that the 36Z15 also handily defeats the X15's Business and High-End scores by margins of 23% and 18% respectively.

The 36Z15's primary target market, however, is that of high-end servers and workstations. Let's take a look at some IOMeter results.

IOMeter Performance

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IOMeter reveals interesting results, splitting between the offerings from IBM and Seagate. While the 36Z15 manages to take top honors in our oft-quoted Workstation Index (a normalized average of Light, Medium, and Heavy loads), the X15 holds its own in the File Server Index and maintains a slim but significant lead in the Database Index. Since File Server differences are insignificant, concentrate on Workstation and Database results.

Constructed from reads and writes of 8k blocks, the patterns are actually quite similar... the Database pattern is wholly random while the Workstation pattern introduces a bit of sequential access as well as emphasizing reads a bit more. IBM triumphs over Seagate in Workstation performance by a margin of 6% while Seagate returns the favor in the Database Index, edging out the IBM by about 3%. It's an interesting contrast in firmware optimizations.


One can hardly expect the best when it comes to heat and noise from a 15k RPM product. Though our review sample thankfully doesn't feature any high-pitch idle noises, seeks grind away louder than all but the earliest 10k RPM drives. The 36Z15 is the hottest drive we've ever tested. Grinding away for about 2 hours in IOMeter, the drive was easily too hot to touch... this even with our PC Power & Cooling Baycool. Active cooling and/or a case with top rate circulation is an absolute necessity with this drive.

The Safe Buy Award

Simply put, this designation means we'd purchase this product without regret. Sure, there may be a slightly better, slightly faster, and/or slightly less-expensive model from a competitor, but you can't go wrong with this particular unit. This award is applicable, of course, to all units at the top of their class, but also applies to units that, though not quite best-of-class, provide a strong showing nonetheless. In conclusion, the Ultrastar 36Z15 easily delivers the best workstation performance we've measured to date. It shatters WinBench 99 WinMark records as well as perfoming solidly in our IOMeter Workstation Index. When it comes to servers and databases, however, the 36Z15 doesn't wallop the first-generation Cheetah X15 as well as many would hope. In the plus column, the drive offers double the capacity of the original X15, and certainly destroys all 10k competition. Just remember, however, that a contender from Fujitsu as well as Seagate's own second-generation unit remain right around the corner.

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