New high areal density 2-and-3 TB Greens from WD

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WD Green 3TB & New 2TB

Dec 7, 2010 by Mike Chin

WD Caviar Green 3TB, 2TB WD20EARS & 2TB WD20EVDS
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US$250; US$100

Western Digital's announcement a few weeks ago of its new 3TB Caviar Green drive brought many issues in the storage sector into sharp relief. A 3TB HDD by itself is not unique. Seagate's 3TB FreeAgent external hard drive has been available since the end of June. That begs the question of why Seagate has still not released the bare 3TB drive.

The answer is contained in a WD document entitled Large Capacity Drives (PDF), which addresses the 2.19 TB barrier imposed by legacy BIOS and the Master Boot Record (MBR) partition table scheme. This document is worth a read if you're looking for a more complete understanding of the 2.19 TB limitation. It's a complicated issue that we posted news on some weeks ago (Sandy Bridge, Bulldozer and UEFI); in a nutshell, the only consistent way to access more than 2.19 TB in a single drive with most current PCs is to use it as a secondary, non-boot, storage drive. Widespead adoption of 64-bit Windows and the new Unified Extensible Firmware Interface (UEFI) — replacing the motherboard BIOS — using Globally Unique Identifier (GUID) partitions will be required before >2.19 TB drives can be used routinely as boot drives. This will come soon enough. It explains why Seagate made the 3TB model available only as an external storage device, for now, and allowed WD to be the first to put a bare 3TB drive on the market. WD did go the extra step of providing an AHCI-compliant host bus adapter (HBA) card with the retail drive kits, to allow the 3 TB drive to be used as a boot drive in a few PCs or as a secondary drive where the onboard SATA controllers/drivers don't provide access to all of the 3TB capacity.

The 3TB Green model had a major impact on our new Silent Server Build Guide, posted just around the time of WD's announcement. Our HDD of choice was the 2TB WD Green, six of them, to be precise, for a 12TB server rig. Now you can get the same capacity with just four drives, with reduced power, heat and noise. The 750 GB/platter density makes for some interesting prospects, such as a 1.5 TB 2-platter drive or a 2.25 TB 3-platter drive — in theory, these should be a couple of decibels quieter than the already amazingly quiet 4-platter models.

These interesting prospects are the reason we have waited till now to post our review of of the 3TB Green: It took a little while for our hardworking rep at WD to get us samples of a new 2TB Green which utilizes three platters, albeit of slightly lower areal density (667 GB/disc) than the 3TB model. This is similar to the new Samsung Spinpoint F4 EcoGreen 2TB, and unlike the previous WD Green 4-platter 2TB models. The point is to tell you about the acoustics and performance of the new 3-platter 2TB drive and the 4-platter 3TB drive and compare them to an older 2 TB Green AV-optimized drive, all in one article. There is a 2.5 TB model available as well, but mechanically, it shares the same 4-platter structure of the 3 TB model, so its acoustics will differ only with sample variance.

WD Green 3 TB on left, new 2 TB WD20EARS in center, older 2 TB WD20EVDS on right.

Same order as above. The recessed casing of the center drive, the new 2 TB WD20EARS, makes it obvious that has fewer platters: 3 versus 4 in the others. The new higher areal density platter drives also share the same smaller controller PCB.

Specifications (from PDF spec sheets)
WD Caviar Green 3TB & 2TB
Capacity 3 TB 2 TB 2 TB
Cache 64 MB 64 MB 32 MB
Interface SATA 3 Gbps SATA 3 Gbps SATA 3 Gbps
Rotational speed* 5400 RPM 5400 RPM 5400 RPM
Heads / Disks* 8 / 4 6 / 3 8 / 4
Avg ready time n/a n/a 14.5 ms
Average latency n/a n/a 4.2 ms
Transfer Rate 110 MB/s 110 MB/s 110 MB/s
Weight* 680 grams 640 grams 740 grams
Power: Read/Write

6.25 W
0.80 W
0.80 W

4.50 W
0.70 W
0.70 W

5.90 W
4.90 W
0.70 W
0.70 W
Quiet Seek

24 dBA
29 dBA
25 dBA

24 dBA
29 dBA
25 dBA

25 dBA
26 dBA
* This information was assessed or derived independently through our testing and research, and is not found in WD specifications.

There are several noteworthy points in the specs:

  1. It's odd that "avg ready time" (the time from when the power is applied until the drive is ready to supply data), random access time and latency are not given for the new WD Caviar Green models.
  2. Not covered in the specs is the fact that the AV optimized WD20EVDS does not have the head park feature of the other drives.
  3. The newer 3 TB drive is 60 grams lighter than the older 2 TB drive, even though they both have 4 platters. Perhaps that weight is accounted for by the bigger controller PCB on the WD20EVDS; perhaps the difference is in the new platters as well.
  4. The absence of a standard seek acoustics spec for the WD20EVDS suggests AAM is locked in quiet mode.
  5. The new 3-platter WD20EARS has reduced power requirements.

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