Skip to main content

Surveillance Hard Drive Shoot-Out: WD And Seagate Square Off

Western Digital Purple

In Western Digital's never-ending quest to snag every color in the rainbow, we now have the WD Purple, which is surveillance-specific. Right under WD's purple banner, there is a large QR code that sends you straight to the drive's webpage.

The Purple is a follow-up to the video- and surveillance-oriented WD-AV GP, which supported WD's SilkStream technology. The purpose of SilkStream was to facilitate up to 12 simultaneous HD video streams utilizing the ATA Streaming Command Set. With the Purple, WD rebrands SilkStream to AllFrame, which now supports 32 HD cameras/channels.

It's interesting to note the way WD is positioning this product. Unlike traditional hard drives, where access times and throughput are prominently displayed, the Purple employs the target market's vernacular, which is number of channels/cameras. To go along with its marketing change-up, WD provides some really nice tools on its website to help guide customers to the correct WD product.

  • Compatibility: Select from over 20 surveillance system vendors and countless models to see which WD hard drives are supported.
  • Product Selector: Select the number of cameras, drive bays, interface, and environment, and WD recommends the best product line.
  • Capacity Selector: Enter the details of the video feeds, and WD lets you know how much capacity your system will require.

Although the Purple is meant strictly for surveillance, WD still recommends the enterprise Se and Re lines for large enterprise surveillance systems. As you will see in our test results, those two families aren't slouches in this segment, either. In fact, they are better than the Purple in almost every way, except for cost. That's really the point of the Purple, though; achieve enterprise levels of performance for a very specific task at a vastly reduced price point. Even though the Purple is well-suited to this particular workload, there are compromises you make.

ApplicationsHome/SOHO/SMBSOHO/SMB/SMESME/Large enterprise
Recommended # of Drives1-86+6+
Typical # of Cameras1-321-64Unlimited
# of ChannelsUp to 32Up to 6464 or more
Workload (TB/year)60180550
Form Factor3.5"3.5"3.5"
Capacity1, 2, 3, 4 TB1, 2, 3, 4 TB250, 500 GB, 1, 2, 3, 4 TB
Power5.1 W9.5 W11 W
MTTF1 million-hr.1 million-hr. rack-mount1.2 million-hr. table-top1.2 million-hr.
PerformanceIntelliPower7200 RPM7200 RPM
RAFF SupportNoYesYes

For those of you who don't spend your days poring over datasheets, the workload rating may come as a surprise. SSD customers are accustomed to seeing a write endurance specification because NAND deteriorates over time, and its useful life can at least be estimated. With rotating media, there is an assumption that enterprise-oriented drives intended for 24/7 operation can be written to all day, every day, for their entire lifespan.

Recently, WD changed the way it rates its drives and now includes that workload specification, indicating how many terabytes of data can be written to the drive per year. Unlike the SSD world, this isn't related to the media's ability to hold data. Rather, it's more closely tied to the MTTF rating. Exceeding WD's number effectively reduces the longevity of the drive, which is guaranteed for three years. But of course, as with SSDs, the higher-quality components required to sustain increasingly taxing workloads drive up cost. The Re family is rated for a workload nine times higher than the Purple, and consequently is more expensive.

The next differentiator is the recommended number of drives. Specific to the Purple, WD suggests no more than eight in a system, and they're not intended for rack-mount applications. This is mainly due to a lack of Rotary Acceleration Feed Forward (RAFF), a technology that overcomes the effects of vibration introduced by other drives in an enclosure. In server applications, where dozens or hundreds of drives can share the same rack, RAFF is necessary. Clearly, WD doesn't believe that functionality is required for the Purple's target market.

For this review, we were not only able to test WD's Purple, but also its Red, Se, and Re, all with 4 TB of capacity.