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Seagate Barracuda 18XL ST318436LW
  March 29, 2000 Author: Eugene Ra  
Evaluation unit provided by Seagate Technology.


To many, 7200rpm SCSI drives are becoming more and more passé. The high-end market, for example, is gearing up for a move to an incredible 15k rpm operation. "Enterprise-class" workhorses will similarly follow suite, eventually moving to 10k rpm spindle speeds. This leaves the poor 7200rpm class as something that will eventually be relegated "only" to ATA drives. But not quite yet...

7200rpm drives have reached a venerable sixth-generation level of refinement. Quantum was first out the door with the Atlas V, an impressive follow up to the Atlas IV,'s 1999 Editor's Choice for a 7200rpm SCSI drive. It's Seagate's Barracuda 18XL, however, that's most intriguing.

The 18XL is a product of transition. Instead of taking the Barracuda series to the next level of capacity (a 36 gig, low-profile product such as the Atlas V), Seagate has chosen to sit back and implement features that will prepare the Barracuda line for a transition to 10k rpm speeds. The 18XL features the same platters found in the Cheetah 18XL/36LP, namely the smaller 3" kind. Up to this point, such smaller platters were found only in 10k rpm units, a side effect of the desire to shave seek times to a bare minimum while also controlling the heat and noise generated by such units.

The flagship Barracuda 18XL features three of these smaller platters, each holding 6.1 gigs of data, yielding a net capacity negligibly larger than the older 'Cuda 18LP. The lack of increased capacity does have its benefits, however. Smaller platters combined with a lower platter count (three for the 18XL vs. the six found in the 18LP) result in a unit that should be in theory much quieter and cooler-running due to reduced spindle motor requirements. Of more interest to many, however, is the resulting seek times. Thanks largely due to the reduced-diameter media, the 18XL sports a specified seek time of just 5.8 milliseconds, the first 7200rpm drive to plumb the sub-six depths. Seagate has also updated the unit's buffer size to a contemporary 2 megs.

Interestingly, Seagate's marketing department seems to have already made a switch, trumpeting 15k drives as the high-end and 10k rpm drives as "mainstream," knocking the poor Barracuda 18XL all the way down the SCSI totem pole to "entry-level" status... a place formerly inhabited only by the dubious Medalist Pro SCSI . Make no mistake, however, the 18XL is an enterprise-class drive, as evidenced by its 1.2 million hour MTBF figure and a five-year warranty. Alright, we can already envision many folks sneering at the MTBF reference but surely the five-year warranty is worth something in an age where other "entry-level" warranties have fallen to 3 years for SCSI disks and 1 year for ATA drives!

The Barracuda 18XL is the first drive to receive an individual review following the rollout of our new testbed. As a result, we're providing figures collected on both the new and old systems. We'll continue to do so for an interim period before phasing out the old testbed entirely.

WB99/Win2k Low-Level Measurements

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Click here to examine the STR graph for this drive

Some interesting things are revealed here. Thanks to smaller platters, Seagate's rated access time (ignoring overhead) for the Barracuda 18XL equals its specified 5.8 millisecond seek time plus a 4.2 millisecond latency that exists for all 7200rpm drives... an access time of approximately 10 milliseconds. The Quantum Atlas V, with its 7200rpm spindle speed and a 6.3 millisecond seek time, features a specified access time of 10.5 milliseconds, a full half millisecond difference in Seagate's favor.

Interestingly, however, the Atlas V soundly defeats the Barracuda 18XL when it comes to access time, by 1.6 milliseconds. When considering overhead, the Atlas V actually beats its own specified seek time by perhaps half a millisecond, while the Barracuda turns in a figure that we'd expect from a drive pushing 7 milliseconds in the seek domain.

The smaller platters found in the 'Cuda hint that the sequential transfer rate in the outermost tracks will be a bit lower than a drive that features full-sized platters such as the Atlas. This does indeed turn out to be the case. While the Atlas V manages to pull 29 megs a second off of its disks in its outermost zone, the Seagate drive manages a bit less than 27 MB/sec. As we've outlined in previous articles, however, sequential transfer rates' influence is important in a minority of applications.

WB99/Win2k WinMarks

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Though the Barracuda 18XL posts better-than-ever figures for a 7200rpm Seagate SCSI drive in WinBench99, it's still no match for the Atlas V, member of a line of drives which lately have thrived in ZD's tests. The Business Disk WinMark 99 reveals the 'Cuda trailing the Atlas by a margin of about 7%. The disparity increases to nearly 15% in the High-End WinMark.

IOMeter Performance

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A quick look at the Linear IOMeter results in the Database Access Pattern confirms that the Atlas does indeed have the faster access time between the two competitors. This advantage, however, melts away in virtually all other IOMeter results.

When it comes to Workstation performance, Seagate's drive shines. In a Linear scenario, the 'Cuda pulls ahead of the Atlas by a margin of nearly 5%. Its advantage increases all the way to a significant 17% under Heavy loads. Similar trends exist under File Server and Database loads.

Legacy Tests

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The Atlas V continues to exercise its proficiency in WinBench99 over the 18XL in tests run on our older testbed. In Windows 95 we find the Seagate drive trailing Quantum's offering by a margins of 12% and 10% respectively in the Business and High-End WinMarks.

Differences in WinMark scores running under NT are remarkably similar to the new-testbed results despite the different operating system and hardware. Here again the 'Cuda falls behind the Atlas by 7% in the Business test and 15% in the High-End.

ThreadMark scores exhibit large gaps. Seagate's unit doesn't fare well in comparison to the Quantum, lagging by margins of up to 33%.


When it comes to noise, the Barracuda 18XL finally breaks tradition with its predecessors. Its lighter actuator seems to result in seek noises that are much less obtrusive than older units such as the Cuda 18LP or 9LP. Idle noise is also undetectable over the power supply's noise.

This drive uses significantly less power than any previous Barracuda model offering the same capacity and it shows. Even outside a drive cooler, the drive runs only warm to the touch in our mid-tower-based new testbed. In our old testbed, featuring its monstrous case, the drive can only be called "cool."

-- 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.Reviews of products such as the Barracuda 18XL highlight the interesting dichotomy that we face as we continue to phase in our new methodologies. If testing were limited to our old testbed, the Atlas V would prove to be a significantly better performing drive than the 18XL. Even on the new testbed, WinBench 99 continues to showcase the Atlas V's prowess. It is, however, in the area of IOMeter results that the Barracuda aggressively fights back, posting higher results in virtually all scenarios. In the end it's a bit of a tough choice, but our heavy weighting of IOMeter leads us to declare the Barracuda 18XL the champion. It's too bad that the 'Cuda doesn't quite live up to its low specified seek time; if such was the case, the victory would have likely been more decisive.

Seagate Barracuda 18XL ST318436LW
Estimated Price: $499
Also Available: ST39236LW (9.2 GB)
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