Oracle Tips by Burleson
Disk I/O Tuning
RAID—Redundant Arrays of Inexpensive Disks
advantages as shadowing and striping at a lower cost. It has been
suggested that if the manufacturers would use slightly more
expensive disks (RASMED—redundant array of slightly more expensive
performance gains could
be realized. A RAID system appears as one very large, reliable disk
to the CPU. There are several levels of RAID to date:
RAID 0. Known
as disk striping.
RAID 1. Known
as disk shadowing or mirroring.
RAID 0/1. Combination
of RAID0 and RAID1. May also be called RAID 10 depending on
whether they are striped and mirrored or mirrored then striped.
It is generally felt that RAID 10 performs better than RAID 01.
RAID 2. Data
is distributed in extremely small increments across all disks
and adds one or more disks that contain a Hamming code for
redundancy. RAID 2 is not considered commercially viable due to
the added disk requirements (10 to 20 percent must be added to
allow for the Hamming disks).
RAID 3. This
also distributes data in small increments but adds only one
parity disk. This results in good performance for large
transfers, but small transfers show poor performance.
RAID 4. 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 RAID 4 is not
considered commercially viable. RAID 3 and 4 are usually are
used for video streaming technology or large LOB storage.
RAID 5. This
solves the bottleneck by distributing the parity data across the
disk array. The major problem is it requires several write
operations to update parity data. The performance hit is only
moderate, and the other benefits may outweigh this minor
problem. However the penalty for writes can be over 20% and must
be weighed against the benefits.
RAID 6. This
adds a second redundancy disk that contains error-correction
codes. Read performance is good due to
The above text is
an excerpt from:
Oracle Disk I/O Tuning
Disk IO Performance & Optimization for Oracle
by Mike Ault
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