NAS System
10
User’s Manual
In summary:
RAID 0 is the fastest and most efficient array type but offers no fault-tolerance. RAID
0 requires a minimum of two drives.
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 5 arrays.
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.
1.4 Array Definition
1.4.1 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.
1.4.2 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.
