FAQ1: How much Paging Space Rule of Thumb?
nagger 100000MRSJ Visits (3775)
The answer is "it depends" and there is no Rule Of Thumb - IMHO.
With machines with large memory, say starting at 64 GB, the memory demand peaks will not go too high nor be too rapid. Suddenly doubling say 1 GB of memory on a small machine with a handful of users, it could happen that three times the number of users arrive or a few large SQL statements run to eat up memory. But doubling a 64 GB machine's memory is very unlikely we don't get 100's of users suddenly logging in at the same minute, nor sudden rises in running 1000's of more SQL statements. It is just maths the larger the resources to slower the rate of change and the lower the peaks above the average. Its the same fact that means large server consolidation projects putting 100's of LPARs on a large box does not see the same urgent peaks of dozens of smaller machines, where one of the boxes runs out of RAM while there is spare capacity in all the others.
If there is a large Oracle SGA or DB2 buffer cache dominating RAM like 30% to 70% - well that is never swapped out, so does not effect paging area. Nor does memory mapped files that a lot of applications use these days.
Then monitor it for 3 months with nmon, of course.
For LPAR with massive RAM, say 1 TB+, I might start with larger paging space, for example 64GB.
I hope that helps, cheers, Nigel Griffiths
ps: For the Performance guru's that demand to tune their paging space within an inch of it's life for small numbers of vital systems and tuning is your whole job have a look at Opti