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Western Digital's Caviar Green 3TB hard drive

The next mechanical milestone comes with complications

Manufacturer Western Digital
Model Caviar Green 3TB
Price (street)
Availability Now

There are two kinds of data in this world: that which we need to access quickly and that which mostly just needs to be stored. In the PC world, the former is typically made up of files associated with one's applications, games, and operating system. You want that data on the fastest drive possible—ideally, a solid-state disk better equipped than mechanical storage to handle the random access patterns commonly associated with OS and application files.

If SSDs were cheap, we'd be using them to store everything. However, flash memory remains an exceedingly expensive proposition next to capacious platters that cost a couple of orders of magnitude less per gigabyte. When you need a lot of capacity for data that mostly just needs to be stored, be it gigabytes of RAW family photos, an MP3 collection fueled by years of rampant piracy, or the complete collection of Sex and the City episodes you ostensibly downloaded for your better half but have yet to delete, only a mechanical hard drive will do. Folks who have already upgraded to an SSD for their OS and application files will want to seek out one of a new breed of low-power hard drives spawned by Western Digital's Caviar GP, which went on to become the Caviar Green.

Introduced more than three years ago, the Caviar GP compromised performance in the name of reduced power consumption and noise levels, while delivering what was at the time a generous terabyte of capacity. SSDs were an even more indulgent luxury back then, but the soon-to-be Caviar Green became an attractive option for folks building home-theater PCs and those in need of quiet, power-efficient secondary storage for their desktops. A new class of hard drive was born, and today, Hitachi, Samsung, and Seagate all have their own spin on the Green recipe.

However, none of them have a drive that can match the latest Green's three-terabyte capacity. Although Seagate was first to reach the 3TB threshold with an external drive released this summer, the hard disk that lives within isn't being offered as a bare Barracuda. Western Digital announced its own 3TB external drive earlier this month, and already, an internal version has become available.

Breaking new ground on the capacity front is nothing new for the Caviar Green family. Back in February of last year, it became the first drive line to reach the 2TB mark. Jumping from two to three terabytes over a year and a half puts one more nail in the coffin of Kryder's law, which predicted a doubling of areal density, and thus hard drive capacity, every year. Western Digital seems intent on being secretive about the areal density of the new platters that fuel its 3TB monster. However, it has confirmed that each one packs 750GB—a 50% increase over the 500GB platters that reside in 2TB Caviars. Those last-gen platters have an areal density of 400 Gb/in², so the new ones are probably squeezing at least 600 gigabits into every square inch of platter surface area.

With 750GB apiece, only four platters are needed to hit three terabytes. A 2.5TB variant is also on the way, but no three-platter model is planned at 2.25TB.

Interface speed 3Gbps
Max drive transfer rate 110MB/s
Spindle speed 5,400 RPM
Cache size 64MB
Platter size 750GB
Available capacities 2.5, 3TB
Idle acoustics 24 dBA
Seek acoustics 25-29 dBA
Idle power 5.5W
Read/write power 6.0W
Warranty length 3 years

Like previous Caviar Greens, this one rotates its high-tech magnetic turntable at about 5,400 RPM. Western Digital has always been reticent to reveal exact spindle speeds for Caviar Greens, which it says are fine-tuned for each capacity point (or, more likely, each platter config) to hit specific power and acoustic targets. However, the company has conceded that this is essentially a 5,400-RPM drive.

Somewhat surprisingly for a product that doesn't aspire to better than "solid" performance, the new Green comes equipped with a substantial 64MB of DRAM cache memory. Western Digital isn't moving the Green line into 6Gbps Serial ATA territory, though. The drive's 3Gbps interface is more than fast enough considering that the spec sheet quotes a maximum disk transfer rate of 110MB/s. However, I wouldn't put too much stock into that number given that the same one is listed for every member of the Caviar Green family, including drives with lower-density platters.

Higher areal densities lead to faster sequential transfers because more data pass under the drive head in a given moment as the platter spins. Thus, the Caviar Green 3TB's 750GB platters should offer higher transfer rates than the 2TB drive's 500GB discs. The amount of available outer-edge area—the fastest portion of a platter—can also affect transfer rates. Since they're both four-platter designs, the 2TB and 3TB Caviar Greens should be even in that department.

Of course, performance is hardly the Caviar Green's raison d'être. This drive is all about quiet, power-efficient storage, and its specs are certainly impressive on that front. We'll test noise levels and power consumption a little later in the review to see how the new Green measures up to the competition.

Like much of that competition, the Caviar Green 3TB is covered by a three-year warranty. That's sufficient, I suppose, but the five-year warranties attached to premium 7,200-RPM hard drives would be a welcome addition to the Caviar Green line. Despite the fact that longer warranty coverage doesn't guarantee a lower failure rate, it would be nice to have the extra coverage for the added peace of mind, however irrational. 3TB is a heck of a lot of data to lose, and reliability is one thing we can't test without delaying this review well beyond the point of irrelevance.

Complications on the road to 3TB
The Caviar Green 3TB makes use of Advanced Format to use the capacity it has available more efficiently. Rather than breaking platters up into 512-byte blocks, Advanced Format relies on 4KB sectors that waste less storage capacity on overhead. Advanced Format is new enough to create compatibility issues with some software, which is why the Caviar Green uses 4KB sectors internally but presents itself as a drive with 512-byte sectors thanks to an emulation scheme WD dubs 512e.

Using 512e is all well and good on drives with capacities less than 2.19TB, but you run into problems with anything larger because Master Boot Record partition tables can only address up to 232 blocks. With 512-byte sectors, that adds up to a maximum capacity of 2.19TB, or considerably less than the 3TB offered by the new Caviar Green. The storage industry's answer to the MBR's addressing limitation is the GUID Partition Table, or GPT, which can address up to 264 sectors. Windows XP doesn't work with GPT partitions, so Western Digital isn't supporting the drive under that OS, although it notes that users may be able to find workarounds using third-party controllers and drivers.

There are issues for users running Windows 7 and Vista, as well. Both support GPT and will detect a full 3TB of capacity when the Green is run as secondary storage. However, if you want to use the Caviar as a boot drive, you'll need a 64-bit version of either OS and a motherboard with a Unified Extensible Firmware Interface (UEFI) BIOS. Motherboards equipped with UEFI BIOSes are few and far between, so Western Digital is shipping this Caviar with a HighPoint RocketRAID 62X Serial ATA card with a PCI Express x1 interface. Folks with motherboards that lack UEFI BIOSes will be able to boot off the drive if it's connected to the HighPoint card, but they'll still need to be running a 64-bit version of Vista or Windows 7 to exploit all three terabytes.

Interestingly, the Caviar Green had no problem booting into Windows 7 x64 when connected to our test system's P55 storage controller. However, this system's motherboard doesn't have a UEFI BIOS, so we couldn't tap the drive's full capacity. 746GB was inaccessible even with the drive converted to GPT, although we didn't run in to any issues getting at all 3TB of capacity with the Green installed as a secondary hard drive.

That was with the Microsoft AHCI drivers built into Windows 7. We had more trouble with Intel's latest RST storage controller drivers, which came out way back in March and are apparently unprepared to cross the 2.19TB threshold. When running the Caviar Green as a boot drive, we could only see 746GB of storage capacity, presumably from the portion of the disk beyond the 2.19TB mark. Even worse, that same 746GB was all that was available when running the Green as secondary storage! Intel is aware of the issue and has committed to address it with an updated RST driver that will be released this quarter. However, you'll still need a motherboard with a UEFI BIOS or a compatible auxiliary storage controller to boot off the Green's full 3TB capacity.

Or you need a Mac. The Cult of Jobs can rejoice knowing that Apple's Intel-based systems have UEFI BIOSes and that OS X 10.5 and 10.6 both support GPT partitions. Those folks should be able to plug in the 3TB Green and use it however they wish.

Watch for motherboard makers to pounce on what looks like an opportunity to differentiate their boards with gaudy "3TB-ready" stickers. Asus has already developed an application that creates a virtual drive to give users access to the Green's full capacity, even under Windows XP. Old XP licenses are great for closet file servers, which seem like a natural home for the first 3TB Caviar.