ArrayMasStor K Series
ÒInstallation Instructions and Procedures.Ó
Copyright
Ó
Advanced Technology and Systems Co., Ltd., 11/2001 Rev. A
13
Trademarks and Trade names that may appear within this document are the property of their respective owners.
NOTE:
One drawback to RAID 1 is that it does not usually allow run-time expansion. Once a
RAID 1 array has been created, to expand it, the data must be backed up elsewhere before
new drive(s) can be added. Other RAID levels generally permit run-time expansion.
RAID 1 is typically simple and easy to implement; however, it is more expensive since twice as
many drives are required for a given amount of usable capacity.
In addition to the data protection RAID 1 provides, this RAID level can also improve performance.
In cases where multiple concurrent I/Os are occurring, these I/Os can be distributed between the
mirrored copies, thus reducing total effective data access time.
RAID 1 (0+1)
RAID 1 (0+1) combines RAID 0 and RAID 1 Ð
mirroring and disk striping.
RAID (0+1) allows
multiple drive failures because of the full redundancy of the disk drives.
If more than two disk
drives are chosen for RAID 1, RAID (0+1) will be performed automatically
.
IMPORTANT:
RAID (0+1) will not appear in the list of RAID levels supported by the controller.
If you wish to perform RAID 1, the controller will determine whether to perform
RAID 1 or RAID (0+1). This will depend upon the number of drives selected for
the logical drive.
RAID 3
RAID 3 implements
block striping with dedicated parity
. This RAID level separates data into
logical blocks, the size of a disk block, and then stripes these blocks across several drives. One
drive is dedicated to parity. If a disk fails, the original data can be reconstructed from the parity
information on the dedicated parity drive.
With RAID 3, the total disk capacity is equivalent to the sum of the capacities of all of the drives in
the combination,
excluding the parity drive
. Thus, for example, combining
four
100 GB drives,
would create a single logical drive with a total disk capacity of 300 GB. This combination of drives
is presented to (and appears as) a single logical drive to the system.
RAID 3 provides increased data transfer rates when data is being accessed in large chunks or
sequentially. However, during write operations that do not span multiple drives, performance is
reduced since the information stored in the parity drive needs to be re-calculated and re-written
every time new data is written to any of the data disks.
RAID 5
RAID 5 implements
multiple-block striping with distributed parity
. This RAID level offers the
same redundancy available in RAID 3; though the parity information is distributed across all disks
in the array. Data and relative parity are never stored on the same disk. If a disk fails, the original
data can be reconstructed using the available parity information that was distributed across the
drives.
