SATA 6Gbit/sec...Does It Double Your SATA Speed?

Artwork: Chip Taylor
Those of us in the business of keeping an eye on new technologies wonder why the buzz about SATA 6Gbit/sec. (a.k.a. Serial ATA Revision 3) hasn't been louder than it is.

SATA 6Gbit/sec. is the next-generation SATA specification and will double the speed of the current SATA standard (which is 3Gbit/sec.). The technology was first demonstrated by Seagate and AMD in March 2009, and is finally coming to market. So why haven't we heard more about it?

Even some hard drive manufacturers are being coy about the new specification. For example, a Western Digital representative, when asked about the company's 1TB SATA 6Gbit/sec. Caviar Black, said that Western Digital had not made a major announcement because SATA Revision 3 just represents an interface change.

Just an interface change? Yes, technically that's correct. SATA Revision 3's speed rating -- like all of the other SATA and Parallel ATA (PATA) ratings -- is actually a measurement of the speed at which data travels from the hard disk's onboard cache to the interface on your PC. It really has nothing to do with the speed of the drive itself.

So is this new SATA technology irrelevant? Not at all. One only has to imagine its use with drives having higher rotational speeds than the current 7,200 rpm (they get to the data more quickly); drives with larger onboard cache (that will hold more data in readiness for the interface to absorb); and even SSDs where none of the offsets of mechanical hard disks exist. It could significantly improve performance in all of those scenarios.

Even with the current crop of drives -- especially with those that have increased cache values of 64MB and up -- SATA 6Gbit/sec. should add some increase in burst speed and sequential reads or writes to contiguous disk sectors. These procedures maximize the continuous streaming of data that a faster interface speed can take advantage of.

To see how much of an advantage this new technology will add, I tested two new SATA 6Gbit/sec. hard drives: The 1TB Western Digital WD Caviar Black ($120) and Seagate's 2TB Barracuda XT desktop hard drive ($260).

Like the new USB 3.0 specification, SATA 6Gbit/sec. is a whole new technology. If you want to use a SATA 6Gbit/sec. hard drive, you'll need a motherboard that provides a SATA 6Gbit/sec. interface (which, if you're building your own system, will cost somewhere between $140 and $240, depending on the type of features you want). If you don't want to replace your motherboard, you can add a SATA 6Gbit/sec. plug-in card, such as the Asus U3S6, to an existing motherboard. Be aware, however, that these cards usually require an x4 PCIe slot and you might be hard-pressed to find an available one in your current PC inventory.

To take full advantage of the technology, you'll also want a system with at least an Intel Core i5 processor (to make use of Intel's SATA 6Gbit/sec.-supporting X55 chip set), at least 4GB of memory and a decent graphics card.

If you're thinking about buying either drive and plugging it into a SATA 3Gbit/sec. motherboard, that's not something I'd recommend. While both of the current SATA 6Gbit/sec. offerings are backward-compatible with SATA 3Gbit/sec., they lose all their advantages in the process.

The Barracuda XT, for example, could only muster 180.1MB/sec. burst speed when it was connected to an older port, but it hit 296.6MB/sec. when attached to its native interface. Write speed was also down somewhat -- the Barracuda XT needed 20 seconds more to complete the write test with the slower interface. (The read speeds with the two interfaces were nearly identical, however.)

Western Digital's Caviar Black suffered a similar fate: Its burst speed dropped from 320.7MB/sec. (using its native interface) to 206.0MB/sec. Its average read time took a small hit, from 112.4MB/sec. to 108.9MB/sec., and its performance in the read test went from 4 minutes, 32 seconds to 5 minutes, 9 seconds. (In this case, write speeds were pretty much the same.)

In fact, all of the 3Gbit/sec. drives were faster reading and writing my data packet than either of the SATA 6Gbit/sec. drives attached to a 3Gbit/sec. interface. That makes a SATA 6Gbit/sec. hard drive a poor choice for either interface type compared to what's already available for data writing or retrieval involving large blocks of information.

Testing the new SATA 6Gbit/sec. drives

I wondered if the Seagate and Western Digital drives could meet or beat each other -- and how they'd fare against a number of different types of 3Gbit/sec. drives. I chose several existing drives to pit them against. These included Western Digital's 2TB SATA 3Gbit/sec. Caviar Black and WD RE4-GP and Seagate's Barracuda LP

I added to these Western Digital's 300GB WD VelociRaptor, a drive with a 10,000-rpm spin rate, universally recognized as one of the fastest SATA drives currently available. And finally, I pitted the new wares against a solid-state drive, Intel's 160GB X25-M.

To test the hard drives, I used three basic tests: SimpliSoftware's HDTach test suite; a file transfer of 8.06GB comprised of 5,089 various files and folders to and from the drive; and a video rendering test to see what effect the destination hard drive has on the process. All of the drives were freshly formatted and without any other content to minimize much of the mechanical overhead.

Note that the Caviar Green and Barracuda LP each have 32MB of cache, the VelociRaptor has 16MB and the remaining 2TB drives were equipped with 64MB each.

This is a lot like Godzilla vs. King Kong. Each of these hard drives has its strengths. The WD Caviar Black has a stronger burst speed (320.7MB/sec.) than the Barracuda XT (296.6MB/sec.). The average read speeds of the two are close, but the Seagate Barracuda XT edges ahead at 115.6MB/sec. compared to 112.4MB/sec.

But where the Caviar Black dropped the ball was during my read/write copying tests. It took 3 minutes, 11 seconds to complete the write portion and 4 minutes, 32 seconds to finish the read portion. In comparison, the Barracuda XT took 2 minutes, 2 seconds and 2 minutes, 36 seconds, respectively, to complete the same tasks. The XT was more than a full minute faster on the write portion of the test and nearly two minutes faster on the read

Surprisingly, the 6Gbit/sec. Caviar Black didn't do much better than its own 3Gbit/sec. version, which needed only 2 minutes, 25 seconds and 2 minutes, 59 seconds, respectively. Of the two, I'd probably recommend the new Caviar Black for small data grabs, like POS (point of sale) transactions that can take advantage of its faster burst speed, while reserving the older Barracuda XT for large record retrievals like graphic files and such.

While SATA 3Gbit/sec. drives from Seagate and Western Digital drives will normally perform better than the average hard disk, it looks like the 6Gbit/sec. drives, while faster than their 3Gbit/sec. counterparts, don't come near to doubling their performance.

The burst speeds are an impressive 320.7MB/sec. and 296.6MB/sec. for the 6Gbit/sec. Caviar and Barracuda. However, the 3Gbit/sec. Caviar Black actually comes close with a burst speed of 248.5MB/sec.

The Barracuda XT's write speed was also impressive at 2 minutes, 2 seconds, but the Barracuda LP came in neck-and-neck with a speed of 2 minutes and 4 seconds. (The 6Gbit/sec. Caviar Black was dead last, by a significant amount, among all of the drives.)

What do we learn from this? That while the SATA 6Gbit/sec. drives do show a performance improvement, it is not necessarily a radical one.

Because the very high-end VelociRaptor spins at 10,000 rpm while the two SATA 6Gbit/sec. drives spin at a "mere" 7,200 rpm, you might suspect that Western Digital's VelociRaptor is destined to be wildly quicker.

You'd be wrong. The XT actually has a moderately faster burst speed than the VelociRaptor (296.6MB/sec. to 261.0MB/sec.) and a moderately faster average read speed (115.6MB/sec. vs. 106.0MB/sec.). The 6Gbit/sec. Caviar Black is also quicker in burst (320.7MB/sec.) and average read (112.4MB/sec.) speeds.

The real rub here, however, is that while the 300GB VelociRaptor is less expensive than the Barracuda XT, it also has 1.7TB less capacity -- and is more expensive than the Caviar Black 6Gbit/sec. with 700GB more storage room. That's quite a lot to give up in either case.

A solid-state drive, having no moving parts to "spin-up" or read/write heads affected by latency, simply must be faster than a mechanical drive -- right? Not necessarily.

Intel's X25-M SSD is one of the fastest solid-state drives currently available. Yet it tied with the 6Gbit/sec. Barracuda XT at the burst speed test (296.6MB/sec.), while the 6Gbit/sec. Caviar Black beat it at 320.7MB/sec. The Intel SSD's average read time of 240.3MB/sec. was better than the XT's 115.6MB/sec. or the Caviar's 112.4GB/sec.

However, with a capacity of 160GB, the Intel SSD holds much less data than the 2TB Barracuda XT and the 1TB Caviar XT. And the X25-M retails around $540 compared to the Barracuda XT's $249 or the Caviar Black's $120.

Bottom line

I'm one of those über geeks from the early days of personal computers. New technology is the shining bauble that immediately attracts my eye and causes an involuntary movement of my hand in its direction. For me there's usually no option. For you, there are several.

I would wait at least four to six months before plunging into SATA Revision 3 technology. That will allow prices to drop a bit and the technology itself to mature. While Seagate has packed the Barracuda XT with 64MB of cache, I believe that 128MB would be better, given the optimal speed of the interface, and I can honestly speculate that Seagate will get here. I suspect that Western Digital will be tweaking the firmware on its Caviar Black as well.

Obviously you can fine-tune the level of performance you can achieve right now in several of the individual test categories by substituting one of the SATA 3Gbit/sec. drives that has the type of performance you need for the applications you're running in place of either of the SATA 6Gbit/sec. hard disks. What you can't do is achieve the overall performance advantage -- which in some cases is admittedly slim -- offered by the 6Gbit/sec. drives themselves.

If you need something right now, Western Digital's SATA 3Gbit/sec. Caviar Black will do the job. It's the Barracuda XT's closest performance competitor among the drives I tested. The 2TB model will cost you about the same as the XT. A 1TB version is available (as well as a 500GB model) for much less, but it will be slower because it only has 32MB of cache.

Also, even with a 32MB cache, the Barracuda LP would be my second choice. At 2TB it's currently priced around $150. You'd end up with the same capacity and reasonable performance at a lower price.

And certainly keep in mind that cutting-edge technology such as SATA 6Gbit/sec. will never get worse than it is now. Typically, all emerging tech tends to get better over time. You have nothing to lose by waiting.

Bill O'Brien has written a half-dozen books about computers and technology. He has also written articles on topics ranging from Apple computers to PCs to Linux, and he has penned opinion columns on IT hardware decisions.

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