RAID

Redundant array of inexpensive disks (RAID) is a technology used for redundancy
and/or performance improvement. It combines several physical disks and aggregates
them into logical arrays. When data are saved, the information is written across all
drives. A RAID appears as a single drive to applications and other devices.
When data are written across all drives, the technique of striping is used. This activity
divides and writes the data over several drives. The write performance is not affected, but
the read performance is increased dramatically because more than one head is retrieving
data at the same time. It might take the RAID system six seconds to write a block of data
to the drives and only two seconds or less to read the same data from the disks.
Various levels of RAID dictate the type of activity that will take place within the
RAID system. Some levels deal only with performance issues, while other levels deal
with performance and fault tolerance. If fault tolerance is one of the services a RAID
level provides, parity is involved. If a drive fails, the parity is basically instructions that
tell the RAID system how to rebuild the lost data on the new hard drive. Parity is used
to rebuild a new drive so all the information is restored. Most RAID systems have hotswapping
disks, which means they can replace drives while the system is running. When
a drive is swapped out, or added, the parity data are used to rebuild the data on the new
disk that was just added.

 

 

 

RAID level 15 is actually a combination of levels 1 and 5, and RAID 10
is a combination of levels 1 and 0.

 

 

 

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