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5.2.1 Recovery log design considerations
Recovery log volume numbers, sizes, and locations affect performance of the
recovery log. The following points should be considered:
All recovery log volumes must be on random access media (that is, disk
drives).
If there is more than one recovery log volume, more than one process can
access the recovery log simultaneously.
If there is more than one recovery log volume, the data is distributed across
all available volumes and writes to the log volumes are performed in a
round-robin fashion. Suppose the recovery log has three volumes, log01,
log02, and log03. A sequence of four writes would go 1 to log01, 2 to log02, 3
to log03, and 4 to log01. Writing in a round-robin fashion distributes the load
and makes the most of available resources.
Create recovery log volumes the same size if possible.
Recovery log segments are 4 MB in size, so a volume must be a multiple of
4 MB. One recommendation is to make recovery log volume sizes a multiple
of the power of 2, that is, 128 MB, 256 MB, 512 MB, and so on.
Tivoli Storage Manager requires 1 MB of space (known as the
the start of the volume.
If you have a number of physical disks (or logical LUNs) allocated for use with
Tivoli Storage Manager, try to position the recovery log volumes on different
file systems, to leverage performance provided by the hardware.
If using mirroring for database and recovery log volumes, and you do not have
enough disks to locate all primary and mirror volumes separately:
– Place primary database volumes on the same physical disks as the mirror
recovery log volumes.
– Place primary recovery log volumes on the same physical disks as the
mirror database volumes.
The total maximum size for the recovery log is 13 GB. That is, the sum of the
sizes of all recovery log volumes must be 13 GB or less.
As an example, say your planning shows that you need 4 GB of recovery log
space. One way to configure this would be to create 8 x 512 MB volumes. Add
1 MB each for the restart area and you have a recovery log size of 4104 MB.
Chapter 5. Database and recovery log
restart area
) at
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