User manual

Chapter 2: Setting up the RaQ XTR
20 Cobalt RaQ XTR User Manual
Support for RAID-0, RAID-1 and RAID-5
A redundant array of independent disks (RAID) is a way of storing the same data
in different places (thus, redundantly) on multiple hard disk drives. A RAID
appears to the operating system to be a single virtual disk drive.
Redundancy means that there is protection against the failure of any single hard
disk drive. Redundant data is used by a RAID system in the event of a failure;
this redundant data can either be a mirror copy or parity data used to reconstruct
the actual data.
The RaQ XTR offers three different levels RAID (depending on the configuration
of the server), each with its own advantages and disadvantages:
• RAID-0 combines the separate hard disk drives into one virtual disk drive
and offers the best performance of the three options. However, the data on
the disk drives is not redundant and the system is thus not fault-tolerant. This
option is available on server configurations with two or more hard disk
drives.
• RAID-1, also known as disk mirroring, consists of a primary hard disk drive
and a secondary hard disk drive; the secondary disk drive is an exact copy or
“mirror image” of the primary disk drive. This option is only available on a
configuration with two hard disk drives.
• RAID-5 includes a rotating parity-bit array. All read and write operations
can be overlapped. RAID-5 does not store redundant data but it does store
the parity information which can be used to reconstruct data in the event of a
single hard-disk-drive failure. RAID-5 requires at least three hard disk drives
for the array.
Although RAID-1 and RAID-5 (but not RAID-0) can protect your data in case of
a hard-disk-drive failure, they do not protect against operator and administrator
(human) error, or against loss due to programming bugs.
The RaQ XTR server implements RAID services through software. Each hard
disk drive has its own independent master channel to allow high performance
without extra RAID hardware.
☞
Important: The RaQ XTR Administrator can set the level of RAID
only through the Setup Wizard.
Once the Setup Wizard process is complete, the level of RAID
cannot be changed unless the system is returned to a factory-fresh
state using an OS restore CD.
Ensure that you have decided on the level of RAID that you want to
implement before launching the Setup Wizard.