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Saturday, June 2, 2007

Seagate's Barracuda ES hard drive

SCSI HAS LONG RULED the enterprise world, but Serial ATA is slowly creeping into corporate server rooms. Serial ATA simply can't be beaten when it comes to storage density, and when you're paying for not only the drives, but also the rack they sit in, density can be an even more important metric than performance.

Today, the highest capacity SCSI drives top out at 300GB—just 60% of the capacity of today's enterprise-class Serial ATA drives, which are available up to 500GB. Seagate has just raised the bar even higher, introducing a new Barracuda ES hard drive with a whopping 750GB of storage. To put that into perspective, consider the storage capacity of a four-drive 1U rack server running RAID 5. With 300GB SCSI drives, you won't even break one terabyte. 500GB Serial ATA drives could give you 1.5TB of redundant capacity, while an array of 750GB Barracuda ES drives would offer a cool 2.25TB, all in the same physical space.

The Barracuda ES owes its freakish capacity to the perpendicular recording technology it shares with Seagate's desktop-oriented Barracuda 7200.10. Physically, the drives are nearly identical. However, the Barracuda ES packs firmware optimizations that promise better performance under more demanding loads, an attribute whose appeal extends beyond the enterprise world and into the enthusiast's realm.

How does the Barracuda ES compare with other enterprise-class Serial ATA hard drives? Is it really any faster than the Barracuda 7200.10? Read on to find out.

What makes an ES?
The Barracuda ES is based on the same drive platters and mechanics as the 7200.10, but it's built to withstand cramped rackmount enclosures where drives can be packed tighter than steerage class on a budget airline. All hard drives vibrate during normal spinning and seek operations, and those vibrations can disrupt the operation of a drive in close proximity by shaking the drive head off its intended path. The disrupted drive must then wait for its head to move back into position before resuming normal operation, resulting in a performance penalty.

To combat vibration-induced performance degradation, the Barracuda ES is outfitted with sensors that detect rotational vibration and adjust the drive head accordingly. These sensors allow the ES to tolerate a rotational vibration of 12.5 rad/second2 with a rotational profile of 20-800Hz. The Barracuda 7200.10, on the other hand, can only tolerate 5.5 rad/second2 between 10 and 300Hz.Apart from the ES's rotational vibration sensors, the drive is physically identical to the Barracuda 7200.10. It uses the same 188GB platters with perpendicular recording and is available with up to 16MB of cache. That cache is programmed a little differently on the ES, of course, but it's the same chip.

In addition to different cache segmentation, the ES's firmware offers a handful of RAID-specific features that you won't find in the Barracuda 7200.10. Among them is Error Recovery Control, which limits the drive's error recovery time to 12 seconds. This prevents prolonged error recovery attempts from causing drives to be prematurely dropped from RAID arrays. Similar functionality is available on Western Digital's enterprise-class Serial ATA drives, although WD recommends disabling the feature for single-drive operation. Error Recovery Control apparently doesn't hinder the Barracuda ES in single-drive systems.

Error recovery is nice, but avoiding errors is even better. To help reduce the number of errors the ES encounters in thermally challenging enterprise environments, the Barracuda ES monitors temperatures and shuffles I/O requests in a manner that allows the drive to cool if it gets too hot. The ES also includes features to simplify multi-drive firmware updates and speed RAID initialization.

Although both the Barracuda ES and 7200.10 are available with a 300MB/s Serial ATA interface, the ES also comes in fibre channel flavors. Those flavors are limited to 400 and 500GB capacities with only 8MB of cache, though.

Hard drive manufacturers seem loath to publish performance specifications for their desktop hard drives, so it's hard to compare the ES's seek times and sustained transfer rate specs to those of the 7200.10. We'll see how real world seek times and transfer rates shake out when we move to our performance benchmarks.

Enterprise-class Serial ATA drives typically offer longer warranties than their desktop counterparts—often five years for enterprise models versus just three years for desktop. Seagate's a little different, though. It offers a five-year warranty for all its internal hard drive products, including desktop and enterprise drives, so the ES doesn't have an advantage over the 7200.10 in this category. Five-year hard drive warranties are pretty standard in the enterprise world, so Seagate certainly isn't skimping. The company's enthusiasm for longer desktop drive warranties has just blunted what could have been another selling point for the ES.

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