22.5 Swap Space Priorities and Performance

   

Every swap area has a priority level, which is a number from 0 to 10. Number 0 is used for the highest priority. If there is more than one swap area in a system, the swap space having the highest priority is used first. When this swap space is full, the next in the row is used, and so on.

In case you have disks of different capabilities installed in your system, it is a good idea to keep the highest priority swap space on the best performing disk.

If two or more swap areas have the same priority, these are used in a round robin fashion. The round robin mechanism is better when all of the disks that contain swap space are of a similar type. In this way, you can distribute data read and write operations among disks used for the swap. This process is called swap interleaving.

If two file system swap areas have the same priority, they are used in round robin fashion as well. However, if a file system swap area and a device swap area have the same priority, preference goes to the device swap area.

As a general guideline, you should use the disks with better data throughput for the swap space. Also, you should try to distribute swap space among a number of disks so that any bottleneck caused by the physical movement of the disk head may be minimized. You should avoid using multiple swap spaces of the same priority on the same disk. In this case, the system will use the swap space in a round robin fashion and there will be a lot of disk head movement. Also, you should avoid using swap space on file systems that are already too busy.


   
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HP Certified
HP Certified: HP-UX System Administration
ISBN: 0130183741
EAN: 2147483647
Year: 2000
Pages: 390
Authors: Rafeeq Rehman

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