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Oracle Tips by Burleson |
Disk I/O Tuning
Chapter 4:
Disk Shadowing or Mirroring
Figure 4-2: Example of Disk
Mirroring
So
far we have discussed basic RAID technology (RAID - Redundant Arrays
of Inexpensive Disks.) RAID can be either software based or hardware
based. Software based RAID never performs as well as hardware based
RAID, in some cases software RAID actually performs worse than
individual disks. RAID controllers are readily available so there is
no need to depend on software RAID.
The main strengths of
RAID technology are its dependability and IO bandwidth. For example,
in a RAID5 array, the data is stored as are checksums and other
information about the contents of each disk in the array. If one
disk is lost, the others can use this stored information to
re-create the lost data. However, this rebuild of data on-the-fly
causes a massive hit on performance. In RAID 1, RAID 10 and RAID 01
failed disks are immediately replaced by their mirror with no
performance hit. This makes RAID very attractive. RAID 5 has the
same
The above text is
an excerpt from:
Oracle Disk I/O Tuning
Disk IO Performance & Optimization for Oracle
Databases
ISBN
0-9745993-4-4
by Mike Ault
Oracle Consulting
Services
Burleson
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