Hardware Reference
In-Depth Information
Drives 2.2TB or larger can also be supported externally via USB without having to resort to GPT
partitioning. This is accomplished within the USB Bridge chipset firmware, which can be designed to
present 2.2TB or larger drives using 4K sectors instead of the normal 512-byte sectors. USB
enclosures or drive docks with this feature can use standard MBR formatting to allow the drive to be
supported in Windows XP with no special software required.
In summary, to use a 2.2TB or larger drive as an internal secondary/data drive, you need to format it
using GPT, and you need to run a GPT-aware OS (Vista SP1 or later). Booting from such a drive also
requires a UEFI BIOS or an enabled UEFI Boot option. You can use GPT-formatted secondary/data
drives with Windows XP by installing third-party GPT support software such as the Paragon GPT
Loader (
www.Paragon-Software.com
).
PATA/SATA RAID
RAID
is an acronym for redundant array of independent (or inexpensive) disks and was designed to
improve the fault tolerance and performance of computer storage systems. RAID was developed at
the University of California at Berkeley in 1987 and was designed so that a group of smaller, less
expensive drives could be interconnected with special hardware and software to make them appear
as a single larger drive to the system. By using multiple drives to act as one drive, increases in fault
tolerance and performance could be realized.
Initially, RAID was conceived to simply enable all the individual drives in the array to work together
as a single, larger drive with the combined storage space of all the individual drives, which is called
a
JBOD
(Just a Bunch of Disks) configuration. Unfortunately, if you had four drives connected in a
JBOD array acting as one drive, you would be four times more likely to experience a drive failure
than if you used just a single larger drive. And because JBOD does not use striping, performance
would be no better than a single drive either. To improve both reliability and performance, the
Berkeley scientists proposed six levels (corresponding to different methods) of RAID. These levels
provide varying emphasis on fault tolerance (reliability), storage capacity, performance, or a
combination of the three.
Although it no longer exists, an organization called the RAID Advisory Board (RAB) was formed in
July 1992 to standardize, classify, and educate on the subject of RAID. The RAB developed
specifications for RAID, a conformance program for the various RAID levels, and a classification
program for RAID hardware.
The RAID Advisory Board defined seven standard RAID levels, called RAID 0-6. Most RAID
controllers also implement a RAID 0+1 combination, which is usually called RAID 10. The levels
are as follows:
