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IBM-AUSTRIA - PC-HW-Support 30 Aug 1999 |
RAID-3 Bit Interleave Data Striping with Parity Disk
RAID-3 Bit Interleave Data Striping with Parity Disk
The use of additional disk to redundantly encode customer's data and guard against loss
is referred to as checksum, disk parity or error correction code (ECC). The principle is the same
as memory parity, where the data is guarded against the loss of a single bit.
Four of the disks hold data, and can be accessed independently by the processor, while the fifth is hidden from the
processor and stores the parity of the other four. Writing data to any of disks 1, 2, 3 or 4 causes the parity to be
recomputed and written to disk 5. If any of the data disks were to subsequently fail, the data can still be accessed by
using the information from the other data disks and the parity disk to reconstruct it.
Since the files are held on individually addressable disks, this design will offer a high I/O rate. Compared to
a single disk of similar capacity, this array has more actuators for the same amount of storage. These actuators will
work in parallel, as opposed to the sequential operation of the single actuator, thus reducing average access times.
RAID-3 (Bit Interleave Data Striping with Parity Disk)
+----------+
| Disk |
|Controller|
+-----+----+
+-----------+----------+---------+-----------+
| | | | |
+--+---+ +---+--+ +---+--+ +--+---+ +---+--+
|Bit 0 | |Bit 1 | |Bit 2 | |Bit 3 | |Parity|
|------| |------| |------| |------| |------|
|Bit 4 | |Bit 5 | |Bit 6 | |Bit 7 | |Parity|
|------| |------| |------| |------| |------|
| | | | | | | | |Parity|
+------+ +------+ +------+ +------+ +------+
Disk 1 Disk 2 Disk 3 Disk 4 Disk 5
Multiple disks are used with the data scattered across them. One disk is
used for parity checking for increased fault tolerance.
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