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Donald K. Burleson
Oracle Tips |
Oracle Redundant Arrays of Inexpensive
Disks (RAID)
RAID0/1. Combination of RAID0 and
RAID1. May also be called RAID10 depending on whether they are
striped and mirrored or mirrored then striped. It is generally felt
that RAID10 performs better than RAID01.
RAID2. Data is distributed in extremely small increments across all
disks and adds one or more disks that contain a Hamming code for
redundancy. RAID2 is not considered commercially viable due to the
added disk requirements (10 to 20 percent must be added to allow for
the Hamming disks).
RAID3. This also distributes data in small increments but adds only
one parity disk. This results in good performance for large
transfers; however, small transfers show poor performance.
RAID4. In order to overcome the small transfer performance penalties
in RAID3, RAID4 uses large data chunks distributed over several
disks and a single parity disk. This results in a bottleneck at the
parity disk. Due to this performance problem, RAID4 is not
considered commercially viable. RAID3 and -4 are usually are used
for video streaming technology or large LOB storage.
RAID5. This solves the bottleneck by distributing the parity data
across the disk array. The major problem is that it requires several
write operations to update parity data. That said, the performance
hit is only moderate, and the other benefits may outweigh this minor
problem. However, the penalty for writes can be over 20 percent and
must be weighed against the benefits.
RAID6. This adds a second redundancy disk that contains
error-correction codes. Read performance is good due to load
balancing, but write performance suffers because RAID6 requires more
writes than RAID5 for data update.
This is an
excerpt by Mike Ault’s book “Oracle
Administration & Management”. If you want more current Oracle tips
by Mike Ault, check out his new book “Mike
Ault’s Oracle Internals Monitoring & Tuning Scripts” or
Ault’s Oracle Scripts Download.
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