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What is RAID?
R.A.I.D
is a term short for
Redundant Array of Independent (or Inexpensive)
Disks. RAID is when two or more hard disks are combined in
way to either increase performance, add data protection (fault tolerance),
or both. It is a very useful technology for today’s high-demand
storage subsystems, with practical and affordable configurations for
everything from home desktop systems to high-end to workstations and
servers.
RAID Levels
Today
there are many choices for RAID configuration, and you must know the
abilities of each type of RAID to choose the right one. It is best to
choose the type of RAID level you need first before choosing a RAID product.
Hardware or Software RAID?
Most forms of RAID can be implemented
in either software or hardware. Hardware RAID just means you use a PCI
RAID controller card or a controller chip built onto your motherboard.
Hardware RAID uses its own BIOS and configuration utility for setup of the
arrays - a utility you must access during system boot process.
Software RAID is a function of the disk management of your operating system.
Hardware RAID is the preferred configuration since it performs independent
of the operating systems installed and does not impact system performance by
using CPU time. Hardware RAID is also more reliable than software RAID
and gives you more options. Software RAID does have a use when you do
not want to spend money buying RAID controller card. |
You can do software RAID (such as striping or
mirroring) using an OS such as NT 4.0 Server or Windows 2000 Server (these
features are not built into NT Workstation or 2000 Professional). To
do software RAID you must first load the OS onto one of the hard drives then
setup the RAID configuration you want in the software.
IDE or SCSI CHANNEL RAID?
You now have the choice to
build a RAID system using either IDE/ATA hard drives or SCSI hard drives.
Standard IDE RAID uses any two IDE hard drive to create RAID 0 (striping) or
RAID 1 (Mirroring) disk array, or more recently you have the option of RAID
0+1 (uses 4 drives to combine benefits striping and mirroring).
Some newer IDE
RAID controllers can do RAID 5 or handle more than 2 to 4 drives, such as
the Promise SuperTrak SX6000. In general, IDE RAID arrays are easier
to set-up than SCSI arrays and just as reliable. IDE RAID provides a
good low cost alternative to SCSI RAID. Promise
www.promise.com , Highpoint Technologies
www.highpoint-tech.com are
leaders in the field of IDE and controllers and IDE RAID cards. You can
even get a motherboard with built-in IDE RAID controller option, giving you
two IDE channels separate from the IDE channel already built into the
chipset.
Still, in some cases IDE RAID is just not
enough. For Corporate/Enterprise Level or Web Servers, very fast data
IO throughput is critical, as is 24/7 reliability. SCSI RAID is the solution
as it offers more options (RAID 0, 1, or 5), more drives that can be
supported per channel or array, faster input/output (especially using Ultra
160 technology), and hot-swap drive bays, and therefore is best suited to
critical server environments where even shutting down the system for 10
minutes is a major problem. Adaptec
www.adaptec.com and Intel www.intel.com
are the primary manufacturers for top-quality SCSI RAID cards. Yes,
there are IDE hot swap and some higher-end IDE RAID cards that can do RAID 5
but in most situations SCSI would be your best option fro hot swap.
Some server motherboards now have the option of
ZCR
(Zero Channel Raid) that allows for a motherboard with onboard SCSI to
be upgraded to SCSI RAID at a lower than normal cost by adding in special
card in the zero-channel slot.
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RAID 0
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