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Saturday, March 9, 2013

The New "NAS" Rated Hard Drives
What's The Difference?

Western Digital has announced a "new" series of hard drives specifically rated for NAS, (Network Attached Storage), devices called "Red" drives.  (See the WD product page here.)  Micro Center has begun selling them, and you can see the web-site ad for them here.  At $114 for a 2 Tb, 7200 rpm, 64 meg cache, 6 Gb/second drive, the price is also reasonable compared to other "advanced" drives - and should come down.

As these gain traction, you can expect other manufacturers to follow suit with their own "NAS" rated drives.

The addition of a new "color" to the current hard drive rainbow is not surprising.  However, the current cacophony of hard drive types, names, colors, and designations can be confusing - so this article hopes to sort some of this confusion into a reasonable order.

Seagate has their Barracuda, Momentus, (etc.), and just plain-vanilla branded hard drives.
Western Digital also has their "vanilla" branded drive, as well as the Green, Black, Blue, "Caviar," "Scorpio," and now their new "Red" drives.

Up until now, the differentiating factor among all these consumer level drives has been power consumption, speed, (including cache size and rpm rating), and retail price-point.

All of these drives, (except for the Red drive), have one thing in common:  They are designed for use in personal computer applications; either desktop, laptop, tablet, netbook, or some other consumer computer product.

In contrast, the new Western Digital "Red" drives are designed to compete with higher-priced Enterprise class drives - at least the Enterprise class SATA drives - in array or RAID configurations, at a much lower price-per-unit.

Hard drives come in two basic flavors:  Consumer drives, intended for the personal computer application, and Enterprise drives that are intended for heavy-duty array based usage.

So, what's the difference?  (Besides the fact that "Enterprise" class drive can be hugely expensive!)

Basically, it's the firmware loaded into the drive.  (At least in the SATA based drives.  Fiber-channel, and other advanced interface technologies are a Horse of a Different Hue altogether.)

Consumer level drives have firmware that assumes that the drive is in an application with little to zero redundancy.

As a consequence, if the drive has trouble reading a sector/cluster on the platter it vigorously attempts to read - and recover - the data, which can take extended amounts of time.  And this is reasonable.  With one, (or at most a few), drives in the system, each one being independent of the others, reading the data - come hell or high water - is of paramount importance.

Enterprise level drive firmware takes an entirely different approach.

Enterprise drive firmware assumes that the drive is in an array or other type of RAID arrangement where data integrity is handled externally to each individual drive - via hardware error recovery, parity, or whatever.  And as a consequence, the firmware on an Enterprise level drive is designed to be less anal about digging for the data.

In other words, it gives up and returns a "data fail" message sooner, (in some cases much sooner), the emphasis being on data throughput speed.  Since there are other drives, or hardware, to handle the, (hopefully!), occasional data error issue, the drive isn't so eager to dig for data.

Additionally - at least in some cases - the drive's reliability and warranty is more highly rated.  (Though there is a white-paper released by Google that claims that the MTBF and speed of the Enterprise level SATA drive is often no better than that of their consumer level counterparts.  Despite their greatly advanced prices.)

So, what does this mean to you?

If you are using the drive in a NAS device, where there is some kind of data-recovery mechanism involved,  the new NAS rated drives might be the best choice.

Though be careful.  If you have a multiple-drive NAS device where the drives are arranged in a RAID-1, RAID-0 or Linear arrangement, (where there is simple mirroring, or all the drives are combined together as one huge drive),"red" drives are not for you, as you still need the built-in aggressive error recovery of the normal consumer rated drive.

Likewise, in a single, (or group of independent drives), arrangement - the NAS rated devices are not the best choice.  If it's performance you want in an independent drive scenario, it's better to spend your money on the performance rated drives.

The big telling point is this:

How important is the ability to recover data on an individual drive?  If there is no external redundancy, then it's absolutely critical.  Otherwise the NAS rated drives might be a better choice.

Note:  No matter how aggressive the error recovery may be, or how advanced the RAID technology, there is no substitute for regular backups.

What say ye?

Jim (JR)

(Stupid Disclaimer:  The names and other descriptive attributes of the drives and manufacturers mentioned above may well be trademarks belonging to their respective manufacturers.)

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