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IBM-AUSTRIA - PC-HW-Support 30 Aug 1999 |
RAID-2 Bit Interleave Data Striping with Hamming Code
RAID-2 Bit Interleave Data Striping with Hamming Code
This type of array design is another form of data striping, and spreads the data across the
disks one bit or one byte at a time in parallel. It is called bit (or byte) interleaving.
Thus, if there were five disks in the array, a sector on the first drive will contain bit 0, 5 and
so on of the data block, the same sector of the second drive will contain bits 1 and 6, and so on.
RAID-2 tries to get around the 50% disk overhead in RAID-1 and provides redundancy by using the
Hamming Code. The error correction bits can be associated with from 4 to 32 or more bits of data. However, the overhead
degenerates to 50% with fewer bits. For example, if data were grouped into bytes, 11 drives in total would be required, 8
for data and 3 for Hamming Code (note: for clarity the Hamming Code drives are not shown in the following figure).
The 8-3 configuration reduces the overhead to 27%.
An array of this design will perform optimally when large data transfers are being done. The host will see the array as a single, or logical drive,
and the data transfer rate will be the product of the number of drives in the array and the transfer rate of the
individual drives.
This design is unable to handle multiple, simultaneous, small requests for data, unlike the previous design so is unlikely to satisfy the requirements
for a transaction processing system that needs a high transaction rate.
RAID-2 (Interleave Data Striping with Hamming Code)
+----------+
| Disk |
|Controller|
+-----+----+
+-----------+----------+---------+-----------+
| | | | |
+--+---+ +---+--+ +---+--+ +--+---+ +---+--+
|Bit 0 | |Bit 1 | |Bit 2 | |Bit 3 | |Bit 4 |
|------| |------| |------| |------| |------|
|Bit 5 | |Bit 6 | |Bit 7 | |Bit 8 | |Bit 9 |
|------| |------| |------| |------| |------|
|Bit 10| |Bit 11| |Bit 12| |Bit 13| |Bit 14|
+------+ +------+ +------+ +------+ +------+
Disk 1 Disk 2 Disk 3 Disk 4 Disk 5
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