9
9
In summary:
RAID 0 is the fastest and most efficient array type but offers no fault-tolerance. RAID 0 requires a
minimum of twodrives.
RAID 1 is the best choice for performance-critical, fault-tolerant environments. RAID 1 is the only
choice for fault-tolerance if no more than two drives are used.
RAID 5 combines efficient, fault-tolerant data storage with good performance characteristics.
However, write performance and performance during drive failure is slower than with RAID 1.
Rebuild operations also require more time than with RAID 1 because parity information is also
reconstructed. At least three drives are required for RAID 5arrays.
RAID 6 is essentially an extension of RAID level 5 which allows for additional fault tolerance by
using a second independent distributed parity scheme (two-dimensional parity). Data is striped on
a block level across a set of drives, just like in RAID 5, and a second set of parity is calculated
and written across all the drives; RAID 6 provides for an extremely high data fault tolerance and
can sustain multiple simultaneous drive failures. It is a perfect solution for mission critical
applications.
1.5 Array Definition
1.5.1 Drive Group
A Drive Group is a group of physical drives attached to the RAID controller, and where one or more
Virtual Drives (VD) can be created. All Virtual Drives in the Drive Group use all of the physical drives
in the Drive Group.
It is not possible to have multiple Disk Groups on the same physical disks. If physical disks of
different capacity are grouped together in a Drive Group, then the capacity of the smallest disk will
become the effective capacity of all the disks in the Drive Group.
1.5.2 Virtual Drive
A Virtual Drive is seen by the operating system as a single drive or logical device. A Virtual Drive is
a storage unit created by the RAID controller from one or more physical drives. If there is an existing
Drive Group and there is available Free Space, then a new Virtual Drive can still be created.
Depending on the RAID level used, the Virtual Drive may retain redundant data in case of a
drive failure.