Storage
Data
Protection
It’s all about recovery; data protection design protects
against all relevant types of failure and minimizes data loss. While disk
capacity has increased more than 1,000-fold since RAID levels were introduced
in 1987, disk I/O rates have only increased by 150-fold. This means that when a
disk in a RAID set does fail, it can take hours to repair and re-establish full
redundancy.
RAID levels:
· RAID-1: An exact copy (or mirror) of a set of
data on two disks.
· RAID-5: Uses block-level striping with parity
data distributed across all member disks.
· RAID-6: Extends RAID 5 by adding an additional
parity block; thus it uses block-level striping with two parity blocks
distributed across all member disks.
· RAID 10: Arrays consisting of a top-level RAID-0
array (or stripe set) composed of two or more RAID-1 arrays (or mirrors). A
single-drive failure in a RAID 10 configuration results in one of the
lower-level mirrors entering degraded mode, but the top-level stripe may be
configured to perform normally (except for the performance hit), as both of its
constituent storage elements are still operable—this is application-specific.
· RAID 0+1: In contrast to RAID 10, RAID 0+1
arrays consist of a top-level RAID-1 mirror composed of two or more RAID-0
stripe sets. A single-drive failure in a RAID 0+1 configuration results in one
of the lower-level stripes completely failing (as RAID 0 is not fault
tolerant), while the top-level mirror enters degraded mode.
For mission critical systems being able to overcome the
overlapping failure of two disks in a RAID set is important to protect from
data loss. RAID 0+1 stripes data across a pair of mirrors. This approach gives
an excellent level of redundancy, because every block of data is written to a
second disk. Rebuild times are also short in comparison to other RAID types.