SSDs get most of the attention, but mechanical hard drives are still a big part of the PC storage industry. Their capacity expands with each new generation, driving down the cost of a gigabyte to just pennies—a full order of magnitude lower than even the most affordable solid-state drives. Thanks to higher bit densities, each new family of mechanical models still tends to offer better performance than the last. Drive makers seem to be paying more attention to acoustics, too, resulting in ever-quieter noise levels.
There is one category in which mechanical hard drives are getting worse, though. Just a few years back, three- and five-year warranties were common. Then, in 2011, Seagate and Western Digital both cut the coverage for most of their internal drives. Two years became the new norm, and the timing left a sour aftertaste. Earlier that year, we'd witnessed major consolidation with the industry as Western Digital acquired Hitachi's hard drive business and Seagate picked up Samsung's HDD division. We'd also watched drive prices skyrocket as massive flooding in Thailand took out multiple production facilities.
These days, five-year hard drive warranties are largely limited to expensive enterprise-class gear. On the desktop, the last remaining hold-outs are Western Digital's VelociRaptor and Black families. We've already covered the former, which occupies unique middle ground between traditional hard drives and SSDs. Now, it's time to turn our attention to the Black.
The top of the line is the Black 4TB, and you can probably guess how much storage it has. The capacity is spread across five 800GB platters, which is a bit of a departure from the norm for WD. The company has traditionally used four-platter designs to hit capacity milestones. It's typically reached those new high-water marks first with low-power 5,400-RPM drives, as well. The Black is indeed WD's first 4TB consumer drive, but it has a much faster 7,200-RPM spindle speed. (Although Western Digital sells a 4TB version of its external My Book series, that product actually uses a Hitachi hard drive rather than one of WD's own design.)
Western Digital hasn't revealed the areal density of the Black's platters. However, we do know the bits are accessed with a dual-stage actuator. The first stage involves the main arm, which gets the drive head in the general vicinity of the desired track. At the tip of the main arm sits a smaller, secondary arm powered by a piezoelectric actuator. This second stage provides more precise fine-tuning. The secondary arm has enough range to cover multiple tracks, allowing "short seeks" to be served without any movement of the main actuator.
As it turns out, the Black isn't the only 4TB drive with five platters and two actuator stages. Hitachi's Deskstar 7K4000 shares those characteristics. The Black 4TB isn't the product of cross-pollination between the Deskstar division and its new parent company, though. Western Digital tells us there's no sharing between itself and Hitachi Global Storage. The two firms are operated as separate companies, although they are at least working together in some capacity on WD's external My Book products.
Like other members of the Black line, the 4TB model has a dual-processor controller chip linked to a 6Gbps Serial ATA interface and 64MB of DRAM cache. A dynamic caching algorithm adjusts how the onboard memory is allocated based on the distribution of read and write traffic from the host system. The cache's 64 megabyte footprint is minuscule compared to the multi-gigabyte flash arrays employed by hybrid storage configurations, so don't get your hopes up. Mechanical drives have had 64MB DRAM caches for years.
Western Digital's higher-capacity desktop models use a StableTrac motor shaft that's anchored at both ends to cut down on vibration. This more secure mounting mechanism is can be found on the 4TB, 3TB, and 2TB Black variants but not on the 1TB and 500GB units. Those lower-capacity models also have lower performance ratings than the 4TB drive, whose sustained transfer rate peaks at 154MB/s. Here are the official specifications:
|Spindle speed||7,200 RPM|
|Max sustained transfer rate||154MB/s|
|Idle acoustics||29 dBA|
|Seek acoustics||34 dBA|
|Warranty length||Five years|
No surprises there. You might be surprised by the $300 street price, though. That works out to about seven cents per gigabyte, which is pretty affordable for a flagship offering with few peers.
There simply aren't many 4TB consumer drives on the market right now. In fact, the WD Black is one of only two with a 7,200-RPM spindle speed. The other is the Deskstar 7K4000, which is no longer listed as a bare drive on Hitachi's site. It appears the WD subsidiary is now focused on selling that Deskstar as part of a retail kit. We've tried for months to get Hitachi to send us one for testing, but despite being told initially that a drive would be shipped out, we've yet to receive the 7K4000.
Seagate has a 4TB drive of its own: the Desktop HDD.15, whose 5,900-RPM spindle speed puts it in a different class of storage products. That model is on its way to the Benchmarking Sweatshop, and we should have a review for you soon.
But I digress. It's time to get back to the Black and see how this mechanical monster performs.