IBM E16RMLL-I Implementation Guide - Page 545
vmtune
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running the vmtune command shown in Example 15-18 (pre AIX V5.2) and the vmo command in Example 15-19 (AIX V5.2 and later). Example 15-18 Tuning pre-5.2 AIX file system cache usage /usr/samples/kernel/vmtune -P50 Example 15-19 Tuning AIX 5.2 and newer file system cache usage vmo -o maxperm%=50 For a detailed explanation of the vmo tunables, please see VMM page replacement tuning under: http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.ibm. aix.doc/aixbman/prftungd/memperf5.htm If, after a period of time, paging still occurs, this may be lowered further. This behavior can also be avoided by using raw logical volumes for the disk storage pools. AIX will not attempt to cache data residing on a raw logical volume and will then be less likely to need to page out application memory. Raw logical volumes are also more efficient (in terms of CPU utilization) since AIX does not spend time attempting to cache this data. If a Tivoli Storage Manager server has high CPU utilization, better performance might be obtained by using raw logical volumes. Often system paging is interpreted as a lack of memory. With Tivoli Storage Manager, this does not happen often, and paging can (and should) usually be eliminated with the tuning above. AIX clients can also benefit from altering the maxperm parameter. During backup, files are read into cache that are not likely to be read again. As before, this can cause application memory to be paged out, causing the main application of that machine to suffer during backup. Lowering maxperm can help with this. Beware of the effects of tuning maxperm on the client application. The performance of the main application may depend on file system cache in some instances (like a file server). In this case it may be desirable to just alter maxperm before and after a Tivoli Storage Manager backup, or not at all. Another tunable parameter is maxpgahead, which controls the AIX read-ahead algorithms. Read-ahead is desirable on the client during backup, and on the Tivoli Storage Manager server during storage pool migration from disk. Chapter 15. Performance considerations 515
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