The reason for the HBA card is that on single 3TB drives companies like
Western Digital and Seagate moved from a 512byte to 4kb sector size. The
main issue here is that older operating systems, in combination with a
legacy BIOS and master boot record (MBR) partition table schemes face a
barrier at 2.19TB. Why? It is 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. One way around this
is to use a larger sector size and this is what the companies have done
by using a 4096byte or 4kb sector size. Western Digital calls this new
sector size Advanced Format (AF) technology. The bad news is that if you
are running Windows XP that this method does not work even with an HBA
card and support is not provided. Windows Vista and 7 users can use an HBA and use a 3TB drive, but get this. Apple OSX fully supports 2.5TB and 3TB drives without any hardware/software hacks. We were told that every Intel Mac PC uses EFI and GUID partitioning. This means that the 2.19TB barrier is a Windows barrier and not a computing barrier in general.
Western Digital provided us with an information sheet about this and you can check it out below.
SATA hard drives are now capable of storing up to 3 TB of data on a single hard drive. At such high capacities certain compatibility issues arise. WD
is leading the way in the industry, providing you with solutions to mitigate these compatibility issues when implementing 2.19 TB and larger drives.
This Information Sheet helps clarify how you can take advantage of the latest in large capacity drive technology on today’s systems with standard
components. WD provides solutions for using current, off-the-shelf systems; you don’t have to wait for the rest of the ecosystem to catch up.
Optimizing Standard Systems for Large Capacity Drives
Limitations of 512-byte Sector Size
Older operating systems such as the Windows® XP computing environment with a legacy BIOS and Master Boot Record (MBR) partition table
scheme encounter a barrier at 2.19 TB because they can address only up to 232 logical blocks x (sector size) capacity and the most commonly
used sector size is 512 bytes. Do the math and you get a capacity limitation of 2.19 TB (2,199,023,255,552 bytes). Some operating systems, such
as Windows XP, only support booting from an MBR (Master Boot Record) partition formatted drive; therefore, there are limitations when attempting
to move to a higher capacity drive. The system’s BIOS and operating system drivers need to agree on capacity and geometry of a hard drive to boot
and operate correctly. Agreement must take place across several software layers to successfully boot a system.
WD Provides Solutions for Moving Beyond 512-byte Sector Size (Greater than 2.19 TB)
Given WD’s areal density leadership, WD is leading the way in providing solutions for drives larger than 2.19 TB by working collectively with industry
partners, system providers, and operating system vendors. Support for drives larger than the current 2.19 TB capacity barrier means implementing
these solutions to successfully integrate high capacity drives.
Considerations for operating systems:
There are several advances in the industry that make large capacity drives possible:
Use Larger Sector Sizes
One way to break the
2.19 TB boundary would be to use a larger sector size and keep the
number of addressable blocks the same. By using sector
sizes of 4096 (4K) bytes this would allow for systems to address a
maximum capacity of 232 x 4096 bytes or 17.59 TB. Unfortunately, WD has
determined through testing that is not feasible at this time due to many
application incompatibilities with devices using sector sizes above 512
However, hard drive manufacturers are working with industry partners to
implement larger native sector sizes in the future.
WD has transitioned to using sector sizes of 4096 bytes or a 4 KB
physical sector size on some hard drive models; this is referred to
Format (AF) technology. Although the drive may be using a sector size of
4096 bytes to store data on the media, it reports and emulates a disk
512 bytes (512e) to avoid application incompatibilities.
Use GPT Instead of MBR
The solution adopted
by the industry is to use GUID Partition Tables, otherwise known as GPT,
instead of Master Boot Record (MBR) partition
tables. UEFI is a community effort by many companies in the computer
industry to modernize the booting process. This partitioning method
provides for up to 18 Exabyte (264) of Logical Block Addressing. UEFI
capable systems are already shipping, and many more are in preparation.
Booting a current Windows operating system from a drive larger than 2.19
TB requires that the system have UEFI support, a 64-bit version of the
OS and will create and use GPT partitions.
The UEFI specification defines a new model for the interface between
operating systems and platform firmware. The interface consists of data
that contain platform-related information, plus boot and runtime service
calls that are available to the operating system and its loader.
these provide a standard environment for booting an operating system and
running pre-boot applications.
Implement WD’s Interim Solutions for Implementing Large Capacity Drives
Existing legacy (non-UEFI) BIOS motherboards and GPT-ready operating systems such as Windows Vista or Windows 7, combined with the
appropriate storage class drivers, can use drives larger than 2.19 TB as secondary storage; but there are a number of host bus adapter (HBA) and
chipset vendors that do not currently offer drivers that support drives larger than 2.19 TB. To provide a solution for these types of compatibility
issues, WD is bundling large capacity WD Caviar® Green™ 2.5 TB and 3 TB drives with an AHCI-compliant HBA that, once installed, allows the
operating system to use a known driver to correctly support large capacity drives. This bundle provides a short-term solution until the time when
updated storage drivers and system software with support for large capacity drives become available.
Illustrative Example: Should an end user decide to add a secondary drive to an existing desktop computer system that incorporates a
chipset such as an Intel-based chipset on a legacy (non-UEFI) motherboard running an operating system such as Windows, the 3rd party
storage class driver may not properly support a drive larger than 2.19 TB. If the large capacity drive is attached directly to the native
motherboard SATA controller, the 3rd party driver may attach to the drive and the driver will not recognize the drive’s full capacity, resulting in an
incompatibility issue. An attempt to uninstall the driver could render the whole system inoperable.
However, when the drive is connected to the WD-bundled HBA, a Windows operating system would load native AHCI drivers that would correctly support large capacity drives and allow normal partitioning and use of the drive.
The example above is only one of many cases where the WD bundled HBA will solve the problem due to an incompatible driver.