Purple Reign: WD Purple Drives


Surveillance gear is becoming as ubiquitous as smartphones these days. From broadcast to baby monitors, from bodegas to Big Brother, you hear and see surveillance in almost every nightly newscast and website. Pricing for surveillance equipment has dropped so much that even big box retail stores, usually in the market to sell you lumber and tools, now sell boxed sets of surveillance equipment.

Once you settle on the surveillance equipment you want or need for your home, small business, or enterprise-level situation, you only need to ask yourself one question: how reliable is your storage solution for those hours of footage? Do you need something that can easily store high-resolution video? Do you just need something that can store still photos?

In other words, where are you going to keep all your data?

WD, one of the leaders in high-tech digital storage solutions, now presents another option in its line of application-specific drives. The WD Purple drive is suited for 24/7/365 operation and comes in 1-6TB configurations. These 3.5-inch SATA III drives all feature a 64MB cache, IntelliPower speed, and All Frame technology. All Frame works with ATA streaming to reduce frame loss, improve playback, and increase the number of drive bays supported (up to eight). All Frame also uses caching algorithms to fine-tune the speed at which your drive runs, so that low bit-rate, high-stream-count applications (like camera footage) will run better and faster on the drive. While WD still suggests its enterprise-level WD Se and WD Re drives for NAS servers, the company has optimized the WD Purple drives to work with security systems that contain up to eight bays and support up to 32 HD cameras, and also contains TLER (Time Limited Error Recovery) streaming support to help improve error coordination between WD drives and RAID controllers.

Another aspect that sets Purple drives apart is their low power consumption, which is critical in stabilizing heat during 24/7 operation (as you know, heat is a drive killer and often causes critical malfunctions in hard drives). The IntelliPower speed also helps in heat dissipation.

Recently, WD sent a WD Purple drive and a surveillance system for us to test over a long period of time (almost three months). The system was a Q-See QT848-4L5-2, and the drive a 4TB model. Our test was to determine the hardiness of the drive and the practical wiping and re-recording over it to see how well it functioned in a 24/7 environment. We used different settings and resolutions for the recording.

I set up the four cameras around the house—two indoors and two outdoors—and connected them to the main DVR unit. I installed the 4TB drive and let it run for an initial eight hours. I then did a check on the quality and consistency of the footage and wiped the information from the drive to start fresh. After the initial test, I ran the surveillance system for 24 hours, 7 days a week, and at the end of each week, I checked the data, wiped the drive, and started again.

This scenario would only apply to a consumer buying one drive for a small four-channel operation. When hooking up more cameras, or recording at higher resolutions, you would have to sacrifice either clarity or quality to fit more data on the drive, which is why you would be better off with multiple drives (WD Purple supports up to eight drives in one system—after that, you’re going to want to look at the enterprise level drives). A 4TB drive will hold a substantial amount of data, but you may want to invest in a multi-drive system if your surveillance needs demand as such. One of the reasons that you can’t use WD Purple drives in systems with more than eight bays is because these drives are not manufactured with RAFF (Rotary Acceleration Feed Forward) technology, a rotational vibration cancellation technology that WD puts in all other drives. RAFF absorbs and compensates for the vibrations caused by server settings.

But multiple drives are still a boon to surveillance. For instance, if you have four cameras and want to store 30 days of footage in MJPEG format, at a resolution of 1024 x 768 and 30 frames per second, you would need almost 35TB of storage. However, reduce the format to H.264, and you’re down to only 6TB of storage. Reduce the resolution to VGA standard 640 x 480, and 24 fps, and you’ll find that you only need 2TB of storage, but the video will be grainy and potentially useless in identifying alleged perpetrators. If you want 30 days of footage stored for up to 32 cameras in prosecution-level resolution, consider employing more than one WD Purple drive.

Our tests were based on four cameras, H.264 format, 1024 x 768 resolution (very high for most businesses, but excellent for home surveillance), and 30 fps (also high; 24 fps will suit most needs). We found that the WD drive handled all video, in all formats, with the same amount of dedication. What did vary was the way that data was parsed out. As you may or may not know, surveillance systems do about 90% of their work writing data, because all a surveillance system really does is store captured footage. Reading back the data is of little importance, because the review of data is done so inconsistently that a read state does not have to perform as well as the write state.

The data-transfer rate on the 4TB drive is posted at 150 MB/s, but as you may know, the maximum rate and the rate you’ll get are going to be different. Using an Intel® Core™ i7 quad-core desktop with 16GB of RAM, the data-transfer rate fell more along the lines of 130 MB/s; not great (the WD Re and WD RED drives are faster) but, again, data transfer is not what these drives are made for. Also, the All Frame innovations will make a huge difference in normal test scores, at times exceeding what a “normal” hard drive will do in the same situation.

We only noticed a slight stutter with higher-resolution playback rates. At 1080p at 30 fps, capture was approximately 5 ms slower than at 720p at 24 fps. With only four cameras to test, we can’t tell you exactly what a 16- or 32-camera system will do to the numbers, but with four cameras running 720p video in H.264 format at 30 fps, we saw very few problems. As a matter of fact, running at 1080p resolution was flawless over several weeks. Every image was crystal clear, every second of footage identifiable (even in low light). The drives were never an issue, even after multiple wipes and reformats. We saw, in total, maybe twenty dropped frames over twelve weeks of testing, which can also be attributed to the surveillance hardware.

All in all, what we saw of the WD Purple drives, including their game-changing All Frame technology, was enough to convince us that WD definitely fills a niche—drives specifically suited to surveillance. 

WD Purple Drives
Capacity 1 TB 2 TB 3 TB 4 TB 6 TB
User Sectors per Drive 1,953,525,168 3,907,029,168 5,860,533,168 7,814,037,168 Not specified by manufacturer
Form Factor 3.5-inch
Advanced Format (AF) Yes
RoHS Compliant Yes
Data Transfer Buffer to Host: 6 Gb/s
Host to/from Drive (sustained): 110 MB/s Host to/from Drive (sustained): 145 MB/s Host to/from Drive (sustained): 145 MB/s Host to/from Drive (sustained): 150 MB/s Host to/from Drive (sustained): 175 MB/s
Cache 64 MB
Rotational Speed IntelliPower
Reliability / Data Integrity
Load/Unload Cycles 300,000
Non-Recoverable Read Errors Per Bits Read <10 in 1014
Power Management
Average Power Requirements Read/Write: 3.3 W Read/Write: 4.4 W Read/Write: 4.4 W Read/Write: 5.1 W Read/Write: 5.3 W
Idle: 2.9 W Idle: 4.1 W Idle: 4.1 W Idle: 4.5 W Idle: 4.9 W
Standby and Sleep: 0.7 W Standby and Sleep: 0.6 W Standby and Sleep: 0.6 W Standby and Sleep: 0.5 W Standby and Sleep: 0.4 W
Environmental Requirements
Temperature Operating Temperature: 32 to 149°F / 0 to 65°C
Non-Operating Temperature: -40 to 158° / -40 to 70°C
Shock Operating (2 ms, read/write): 30 Gs
Operating (2 ms, read): 65 Gs
Non-Operating (2 ms): 350 Non-Operating (2 ms): 250
Acoustics Idle: 21 dBA Idle: 23 dBA Idle: 23 dBA Idle: 25 dBA Idle: 25 dBA
Seek (average): 22 dBA Seek (average): 24 dBA Seek (average): 24 dBA Seek (average): 26 dBA Seek (average): 26 dBA
Dimensions (HxWxL) 1 x 4 x 5.8" / 2.5 x 10.2 x 14.7 cm
Weight 0.99 lb / 0.45 kg 1.40 lb / 0.64 kg 1.40 lb / 0.64 kg 1.50 lb / 0.68 kg 1.65 lb / 0.75 kg

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Your understanding of "IntelliPower" ("a rotational speed that ramps as high as 7200 rpm during high usage, and as low as 5400 rpm for shorter, less intense tasks") is incorrect (as is designed by vague, disingenuous WD marketing.)  Intellipower drives spin at 5400 RPM, fixed rate.

IntelliPower is the WD marketing name for a particular choice of spin speed, caching algorithms, and transfer rates that WD uses to indicate a drive has a low power draw combined with good performance characteristics. The inference is that pure rpm numbers alone don't provide an adequate picture of a drive's performance.  For certain operations, a fixed speed 5400 RPM drive can be as performance effective as a 7200 RPM drive, (sequential read/writes), and for other operations is more limited by the 5400 RPMs (random access operations.)  But again, the spin rates of these drives are 5400 RPMs, fixed, NOT variable.

Dear Reader,

After further review, we are striking the comment – Intellipower does not vary spin speed while in use. It does indeed have a fixed spin speed while running, and the only variance, according to WD, is that “these may vary with individual drive capacity points within a particular drive model.” We apologize for the error.