Western Digital's campaign to delineate hard drive market segments and the accompanied colour-based branding has proved to be very popular. The Red drive lineup for the SMB / SOHO NAS market and the Black drives for the enthusiast segment have been greeted with good market acceptance. Today, Western Digital is expanding this initiative with the Purple branding for hard drives targeting the growing surveillance market (NVRs and NAS units dedicated to recording feeds from IP cameras).


All SATA hard drives fulfill the same basic functionality of storing data on platters. Most hard drives use the same hardware circuitry (except for enterprise drives which have features such as RAFF - Rotary Accelerated Feed Forward - that require extra sensors on the drive to better handle vibrations in storage arrays). The scope for differentiation boils down to the firmware. The SATA protocol has a number of optional features intended to improve performance for specific scenarios. One example is NCQ (Native Command Queuing), which allows for reordering of commands to improve efficiency. Another example is the ATA Streaming Command Set, which targets A/V setups by providing features targeting video payloads. Drives targeting the A/V and surveillance markets can optimize the firmware around this optional specification.


Western Digital has been serving the DVR / STB / surveillance storage market with the WD-AV GP product line for quite some time now. Hardware-wise, these drives happen to be the same as the Green drives, but the difference happens to be in the firmware. WD's ATA Streaming Command Set implementation under the SilkStream tag supports up to 12 simultaneous HD streams.

Most NVRs are based off NAS platforms in RAIDed environments. Since the WD-AV-GP drives were not specifically geared for use in NAS devices, it makes sense for WD to develop firmware optimized for video surveillance storage using the Red drives as the hardware base. The result is the WD Purple lineup.

Features and Specifications

The Purple hard drives (WDxxPURX) are dedicated to service the surveillance market. Similar to the WD-AV GP lineup, these are also built for 24x7 operation. The SilkStream tag for the optimized firmware in the WD-AV GP lineup is replaced by AllFrame in the WD Purple. The optimizations work with the ATA Streaming Command Set to improve playback performance and reduce errors / frame loss. While SilkStream was advertised to support up to 12 simultaneous HD streams, AllFrame is designed to support up to 32 HD cameras / channels. Obviously, advantage of the AllFrame technology is possible only with the host controller support. It goes without saying that the appliance vendor must be in the compatibility list provided by WD in order to take advantage of the surveillance-specific features in the Purple drives.

Similar to the Red drives, these come with the IntelliPower feature (rotational speed of 5400 rpm) and TLER enabled. IntelliPower enables WD to provide best-in-class power consumption numbers with the Purple drives. There is no RAFF support on-board, though, as these are meant for table-top appliances with 1 to 8-bays. The drives are rated for workloads up to 60 TB/yr. For reference, recording 4 x 1080p30 streams for 365 days requires 200 TB of storage. SD streams come with lower storage cost. In any case, putting the WD Purples in RAID with multiple drives should easily keep workloads for each drive under 60 TB/yr. For SMB / SME surveillance setups requiring up to 64 cameras, WD suggests the use of Se drives, while mission-critical applications are advised to utilize the more powerful Re drives.

The 3.5" Purple drives come in 1, 2, 3 and 4 TB capacities. WD has a number of launch partners including, but not limited to, PELCO, HikVision, Synology and QNAP.

In other news, Seagate also announced the Surveillance HDD yesterday, targeting the surveillance market. Unfortunately, we weren't briefed extensively about it, but the specs seem similar to that of the Purple lineup (except for the addition of RV - rotational vibration - sensors for operating in multi-drive environments, which seems similar to RAFF technology).



Source: Western Digital

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  • pixelstuff - Tuesday, February 25, 2014 - link

    Or even better release a generic drive, with maybe three build quality levels, and provide upgrade-able or swap-able firmware to fit the situation.
  • Sivar - Tuesday, February 25, 2014 - link

    What's the difference between "512e" and "512n" format?
    Does 512n mean that the hard drive "n"atively uses 512 byte sectors? If so, isn't that sort of a bad idea for a mission-critical drive? Among other benefits, 4k sectors allow for better ECC.
    Perhaps compatibility issues led to the choice.
  • shodanshok - Wednesday, February 26, 2014 - link

    512n (or 512B) drivers have real 512 byte sectors.
    512e drivers have emulated 512 byte sectors, while real sector size typically is 4K.

    For archiving, 4K drivers (or 512e, if you prefer) are perfectly fine, even in enterprise environment. However, when using virtual machine and/or database software (both issue many small sub-4K writes), 4K drivers have lower performance then their 512B cousins. A good battery-backupped RAID card can alleviate the performance differences, still 512B disks are the better choice for "live" vm/db enterprise environment.

    Regarding the reliability, ECC alone say very little. For example, the 4K RED disk have a BER (Bit error rate) of about 1/10^14, the 4K SE have a BER of 1/10^15 and the 512B RE have a BER of 1/10^16. In other word, the RE bit error rate is 100 time lower then the RED BER.

  • douglaswilliams - Tuesday, February 25, 2014 - link

    Is the 60 TB/year workload rating good for all the drive capacities (1, 2, 3, & 4TB)?

    If so, does that mean that the controller will be what most likely fails, rather than the platters or the write heads, or some weird magnetic sector corruption (I might have just made that up), etc.?

    Also, does the drive log your total throughput (like SSDs) so that they can deny your warranty if you go over the workload limit?
  • DanNeely - Tuesday, February 25, 2014 - link

    Like SSDs where the write limit is listed the same for all capacities, it just means they only tested them all to the same low standard.
  • riggo49 - Wednesday, February 26, 2014 - link

    What's really strange is that their marketing guys need to take a basic math course. A 32 camera HD (1080) H264 system would generate over 1,000 terabytes of data a year at 30 frames per second. Divide that by the maximum number of drives (8) and you end up writing 120 terabytes a year to each drive. Learn to math!!!
  • Beany2013 - Tuesday, February 25, 2014 - link

    Did anyone tell Western Digital how stupid it was to have a product range called Red and a product range called Re?

    I had to sniff through their website to differentiate between the two.

    Or am I just an old school kinda guy who thinks that different products should have actual different names?

    But then I thought the Ford Cougar/Kuga thing was stupid too. Because it is.

    Just give us a drive capable of decent MTBF and let us choose the required firmware and apply it over a shell script we can run over a NAS-vendor-approved update (most of 'em run Linux) and leave it be.
  • iAPX - Saturday, March 1, 2014 - link

    Happy to see that WD is investing into mass-surveillance, instead doing good hybrid drives :)
  • zata40 - Tuesday, March 4, 2014 - link

    Really they're just updating an existing line of drives and adding TLER for the NVR market.

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