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AG-7.2.B1-092414 • Restricted - customer use only
7
RAID
DISK
DRIVE
ARRAY
RAID, an acronym for "Redundant Array of Independent Disks,” is a storage technology that
combines multiple hard drives so that data can be stored on them as if they were one logical unit.
RAID takes multiple physical disks and makes them appear and function as a single hard disk drive.
Most RAID configurations support write caching. Write caching improves write performance by
caching write data in memory and then copying data to the disk array. These systems include battery
backup of controller memory to prevent data loss or corruption in the event of a power failure.
Except for the smallest system types (Scout), all MIP servers use some form of RAID to insure data
integrity. Depending on configuration three RAID variants: 1, 5, and 6, are used.
Volicon, a division of Verizon Digital Media Services uses Enterprise class SATA drives for maximum
performance and reliability.
7.1
RAID Variants
RAID 1
RAID 1, or disk mirroring, is the process of replicating the data to more than one disk. Both the disks
are operational at the same time, so the system can read data from both simultaneously. This
enhances the speed of read operations. However, the write operations are slower as the system
executes each write operation twice, once on each disk. A minimum of 2 disks are required for a
RAID 1 array.
RAID 5
RAID 5 can tolerate failure of any drive in the array without losing a single byte of stored data. RAID 5
is block-level striping with distributed parity. Striping and data are distributed by independent read
and write operations. In a "write" operation, data to be recorded is striped across all array members
interspersed with a parity block and distributed so as to place one segment containing the parity
checksum on a different drive within each striping cycle. Sometimes defined as rotating parity, this
scheme is the reason why it doesn't matter which drive in the array fails. A minimum of 3 disks are
required for a RAID 5 array.