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Oracle Tips by Burleson |
Disk I/O Tuning
Chapter 4:
RAID—Redundant Arrays of Inexpensive Disks
Table 4-1 shows how
Oracle suggests RAID should be used with Oracle database files.
|
RAID |
Type of Raid |
Control File |
Database File |
Redo Log File |
Archive Log File |
|
0 |
Striping |
Avoid |
OK |
Avoid |
Avoid |
|
1 |
Shadowing |
Best |
OK |
Best |
Best |
|
0+1 |
Striping and
Shadowing |
OK |
Best |
Avoid |
Avoid |
|
3 |
Striping with
static parity |
OK |
OK |
Avoid |
Avoid |
|
5 |
Striping with
rotating parity |
OK |
Best if RAID0-1
not available |
Avoid |
Avoid |
Table 4-1:
RAID Recommendations (From Metalink NOTE: 45635.1)
Properly setup RAID allows much higher performance than just a bunch
of disks (JBOD.) For the same volume a RAID 5, RAID 1-0 or RAID 0-1
array delivers a higher IO bandwidth than a JBOD array. However,
remember from chapter 3 that only one device can communicate over a
SCSI bus at the same time. Therefore if you have multiple SCSI
chains you should strip across chains not along chains. In a SCSI
based arrays disks are often arranged in what are known as trays (or
sometimes bricks) with each tray of eight disks formed from a single
SCSI bus. the buses in the SCSI array are then grouped on the SCSI
array backbone which is usually fibre based (1-2 gigabit/sec
capacity.) In addition to the additional command latency issues that
would occur if multiple devices in the same chain where striped
together, If you stripe along chains you could overload the SCSI bus
for MB/sec. Figure 4-4 shows this concept.
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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