Chapter 1. Introduction to the 3ware Command Line Interface
10
3ware 9000 Series Serial ATA Controller CLI Guide
Understanding RAID Concepts and Levels
The next few pages introduce RAID concepts you may find useful. For
additional information about installing and managing your 3ware controller,
see the user guide that came with your 3wae RAID controller.
3ware controllers use a Redundant Array of Inexpensive Disks (RAID) to
increase your storage system’s performance and provide fault tolerance
(protection against data loss).
The following concepts are important to understand when working with a
RAID controller:
Arrays and Units
. In the storage industry, the term “array” is used to
describe two or more disk drives that appear to the operating system as a
single unit. When you work with 3ware software, “unit” is the term used
to refer to an array of disks that is configured and managed through the
3ware software. Single-disk units can also be configured in the 3ware
software.
Mirroring
. Mirrored arrays write data to paired drives simultaneously. If
one drive fails, the data is preserved on the paired drive. Mirroring
provides data protection through redundancy. In addition, mirroring using
a 3ware controller provides improved performance because 3ware’s
TwinStor technology reads from both drives simultaneously.
Striping
. Striping across disks allows data to be written and accessed on
more than one drive, at the same time. Striping combines each drive’s
capacity into one large volume. Striped disk arrays achieve highest
transfer rates and performance at the expense of fault tolerance.
Distributed Parity
. Parity works in combination with striping on RAID 5
and RAID 50. Parity information is written to each of the striped drives,
in rotation. Should a failure occur, the data on the failed drive can be
reconstructed from the data on the other drives.
Hot Swap
. The process of swapping out a drive without having to shut
down the system. This is useful when you need to swap out a degraded
drive, manually or automatically, with a pre-designated spare.
Array Roaming.
The process of swapping out or swapping in a
configured unit without having to shut down the system. This is useful if
you need to move the unit to another controller.
Disk Roaming.
The process of removing a unit from a controller and
putting it back later, either on the same controller, or a different one, and
having it recognized as a unit. The disks may be in a different order than
they initially occupied, without harm to the data. The disks may be
attached to the same ports or different ports on the controller.
