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Seagate's NAS HDD 4TB reviewed

Meet the Desktop HDD.15's RAID-optimized twin
— 2:52 PM on October 10, 2013

Product segmentation is a delicate art that tech companies have come to master. We see it in the semiconductor industry, where chip makers derive a range of products from the same base silicon. Clock speeds are tweaked, functional units are trimmed, and switches are flipped to remove certain features.

The same sort of thing happens in the storage world. Drive platters are shared between hybrid SSHDs, high-performance 7,200-RPM hard drives, and low-power models with slower spindle speeds. Some drives are tuned for typical client workloads, while others are optimized for RAID implementations and network-attached storage.

Seagate's lineup is perhaps the best example of this kind of segmentation in action. The same 1TB platters can be found in the Desktop SSHD 2TB, the 7,200-RPM Barracuda 3TB, and the 5,900-RPM Desktop HDD.15. The Desktop HDD.15 is meant for desktop systems, and it has a NAS-centric twin geared toward external storage arrays and internal RAID configs.

On the surface, the NAS HDD 4TB looks identical to its Desktop HDD.15 sibling. Were it not for the labels, you'd have a hard time telling the two apart.

The NAS HDD 4TB (left) and the Desktop HDD.15 4TB (right)

The mix of components on the associated circuit boards is different—but only slightly. You're basically looking at two versions of the same drive. The thing is, the NAS HDD sells for $220, while the Desktop HDD.15 rings in at only $170. What gives?

A few things, actually. The NAS HDD is covered by a three-year warranty, while the Desktop HDD.15's coverage runs out after only two years. Longer warranty coverage doesn't necessarily translate to better reliability, of course, but the accompanying specifications suggest the NAS HDD is more robust than its desktop counterpart. The NAS drive is rated for twice as many load/unload cycles and more than three times the number of power-on hours as the desktop model. It's also certified for 24x7 operation, a blessing not bestowed upon the Desktop HDD.15.

Next on the list: validation testing for a wide range of network-attached storage devices. The NAS HDD offers guaranteed compatibility with scores of different NAS boxes from 10 different device providers. The drive is only qualified for devices with up to five bays, though. Seagate has enterprise-oriented models with additional features targeting servers and storage devices with more bays.

The "NASWorks" umbrella covers the rest of the NAS HDD's unique attributes. This marketing term encompasses a number of capabilities, including vibration minimization, power management, and error recovery.

All mechanical hard drives vibrate to some extent. That's usually not a problem for well-anchored drives in desktop systems. However, vibration can compromise performance and reliability when multiple drives are tightly packed into the small enclosures typical of NAS boxes. In the NAS HDD, "dual-plane balance" tech aims to reduce vibration by "better balancing the drive motor." Seagate also says the drive has "better components for vibration tolerance" than the Desktop HDD.15.

On the power management front, the NAS HDD is governed by custom rules about when to engage sleep and standby modes. NAS devices can have different expectations than desktop systems about how readily data should be accessible. NASWorks takes those preferences into account while still pursuing low-power states.

NAS devices also have different expectations surrounding error recovery, a trait they share with desktop RAID configurations. If a drive spends too long chasing down an error, it can be marked as bad or unresponsive and dropped from the array. Even if the drive is undamaged, rebuilding the array can be time consuming, and performance will almost certainly be compromised until the rebuild is complete. NASWorks includes time-limited error recovery to prevent premature disconnects, leaving the NAS device or RAID controller to pick up after any error recovery attempts that are cut short.

Support for the ATA Streaming command set isn't explicitly tied to NASWorks, but it might as well be. This optional component of the ATA specification allows hosts to demand data on a specific timeline. ATA Streaming commands are used by some consumer electronics devices, and as far as I can tell, they're not supported by the Desktop HDD.15. The other NASWorks perks I've mentioned aren't available on the desktop drive, either.

Interface 6Gbps SATA
Spindle speed 5,900 RPM
Cache size 64MB
Platter capacity 1TB
Total capacity 4TB
Max sustained data rate 180MB/s
Average read/write seek time < 12 ms
Typical idle power 3.95W
Typical seek power 4.8W
Idle acoustics 2.3 bels
Operating acoustics 2.5 bels
Warranty length Three years

Seagate says the NAS HDD's firmware has been tuned to balance sequential and random performance. The drive's maximum sustained data rate matches that of the Desktop HDD.15. However, the desktop drive has quicker average seek times: less than 8.5 ms for reads and under 9.5 ms for writes, both notable improvements over the sub-12-ms figure quoted for the NAS HDD. We'll get to our own performance tests in a moment, but first, I have a bone to pick.

Apparently following WD's IntelliPower example, Seagate appears to be obfuscating the NAS HDD's spindle speed. The rotational speed isn't referenced anywhere in the product documentation, so we had to ask Seagate for clarification. The manual does quote the drive's average latency as 5.1 milliseconds, which matches the latency of the 5,900-RPM Desktop HDD.15, so there's at least enough information to work backward to an answer.

Although I get that consumers don't need to be inundated with numbers they may not understand (and that may be somewhat less relevant for low-power offerings that don't focus on performance), it's silly that drive makers have become hesitant to reveal such a defining specification in their datasheets. Only nerds look at those documents, and making us extrapolate the spindle speed from the rotational latency seems unnecessary.

Anyway, enough with that tangent. Let's move on to our performance results.