NETGEAR RNDP6620-100NAS - ReadyNAS Pro RNDP6620 Business Edition Software Manual page 126

• RAID 5 (striped disks with parity) combines three or more disks in a way that protects
data against loss of any one disk; the storage capacity of the array is reduced by one
disk.
• RAID 6 (striped disks with dual parity; less common) can recover from the loss of two
disks.
• RAID 10 (or 1+0) uses both striping and mirroring. "01" or "0+1" is sometimes
distinguished from "10" or "1+0": a striped set of mirrored subsets and a mirrored set
of striped subsets are both valid, but distinct, configurations.
RAID can involve significant computation when reading and writing information. With
traditional "real" RAID hardware, a separate controller does this computation. In other cases
the operating system or simpler and less expensive controllers require the host computer's
processor to do the computing, which reduces the computer's performance on
processor-intensive tasks. Simpler RAID controllers might provide only levels 0 and 1, which
require less processing.
RAID systems with redundancy continue working without interruption when one (or possibly
more, depending on the type of RAID) disks of the array fail, although they are then
vulnerable to further failures. When the bad disk is replaced by a new one, the array is rebuilt
while the system continues to operate normally. Some systems have to be powered down
when you remove or add a drive; others support hot-swapping, allowing you to replace drives
without powering down. RAID with hot-swapping is often used in high-availability systems,
where it is important that the system remains running as much of the time as possible.
Note: RAID is not an meant to be an alternative or substitute for backing
up data. Data might become damaged or destroyed without harm to
the drive or drives on which they are stored. For example, part of the
data might be overwritten by a system malfunction; a file might be
damaged or deleted by user error or malice, and not noticed for days
or weeks; and, of course, the entire array is at risk of physical
damage.
ReadyNAS for Business RAIDiator 4.2.17
Understanding RAID
126