WD Caviar Green 3TB Hard Drive Review

Breaking the 2.19TB Barrier

Unfortunately, if you're still using Windows XP, don't expect your system to make full use of any 3TB drive (yet). The problem is that older operating system, in combination with a legacy BIOS and master boot record (MBR) partition table scheme face a barrier at 2.19TB. Why? It's because they can only address up to 2^32 logical blocks, multiplied by sector size capacity. Since the most commonly used sector size is 512 bytes, mathematics tells us there is a capacity limit of 2,199,023,255,522 bytes or 2.19TB.

Advances in technology make the use of large capacity drives possible. One way would be to use a larger sector size, while keeping the number of addressable blocks the same. For example, using 4096 (4k) byte sectors would allow for systems to address a maximum of 2^32 x 4096 bytes, or 17.59TB. Unfortunately, there are too many application incompatibility issues when you go over 512 bytes.

Western Digital has made the transition to physical sector sizes of 4096 bytes and calls it Advanced Format (AF) technology. To address the problem associated by making this move, the hard drive reports and emulates a disk using 512 bytes.

Another solution is to utilize GUID partition tables (GPT) instead of master boot record (MBR) tables. While MBR restricts a disk's partition size to 2.19TB, GPT allows for a maximum size of 9.4 zettabytes. GPT forms part of the extensible firmware interface (EFI) standard and is Intel's proposed replacement for the BIOS.

Hopefully you like acronyms because we're going to throw some more your way. The EFI specification is governed by the Unified EFI forum. UEFI defines a new way for operating systems to work with system platform firmware. It's a community effort by a group of companies within the industry to bring the legacy booting process up to date. It's unlikely the motherboard in your system today supports UEFI, but according to Western Digital, most systems shipping now through Q2 2011 will be UEFI capable. 

Existing motherboards utilizing BIOS (non-UEFI), GPT ready operating systems like Windows 7 64-bit, and appropriate storage class drivers can use hard drives larger than 2.19TB as storage. A problem is a number of host bus adapter (HBA) and chipset vendors don't offer driver support for these types of drives.

To provide a solution for this compatibility issue, Western Digital bundles an HBA with the Caviar Green 3TB drive that allows the operating system to use a known driver to correctly support extra large capacity drives. Granted, this bundle is a short term solution until updated storage drivers and system software support become available industry wide. 

Early adopters should not disregard the bundled HBA. If you decide to add the Caviar Green 3TB as a secondary drive to your existing system that incorporates, for example, an Intel chipset on a non-UEFI mobo, the third party storage driver may not properly support it. If the drive is directly attached to the board's SATA port, the storage driver will probably not recognize its full capacity. In addition, any attempt to uninstall the driver could render the system inoperable. Bottom line is to make sure you use the bundled HBA for now. 

As with every hard drive, you can use the Caviar Green 3TB as a primary boot drive, or a secondary storage option. Just know that booting a current Windows operating system from any drive larger than 2.19TB requires a UEFI capable motherboard and a 64-bit version of the OS. We've only been able to verify a handful of consumer boards that support UEFI (several Intel models and one from MSI), so think of this drive as a secondary storage solution as of right now. 

Related content