Don't panic!

AIX is very good at keeping memory full with all sorts of things it believes will be useful. If something is not needed now, there is no reason to actually scrub memory unless another process is allocated that address to work in. I used to worry about this too. It can (as you suggest) be used for all sorts of caching. It is faster than reading from the disk, but there is no point in paging it out, so it just gets lost if not used. When a process then needs the data, it is just read from disk as normal, which is no different than paging back in (unless you have wildly different performance disks) but to use the paging, it would have to keep a record that it existed etc., so it's more effort to page this kind of thing.


Basically, if the server is not paging, then it is fine.


There used to be a rule of thumb for double paging space for your RAM. Then that changed (even less formally if that's possible) to double RAM for the first 2Gb, then 1Gb for the rest of your RAM allocation.

Of course, what you really need to estimate is the total space you will need and balance the cost against the speed of real memory. Beyond what you can justify paying for, allocate paging to cover it, and a bit more to be sure. Very inexact though. Have some sort of monitor that check paging space, either have a regular look with lsps -a or vmstat, sar or other tools just to keep a check on how much you are really using.

If you are paranoid about crashing the server, allocate lots extra paging space, but don't try to grow /dev/hd6. If you succeed, you will never be able extract it without considerable effort.

If you allocate 2Gb chunks as paging00, paging01, paging02 ....etc., then when your service is settled, you can work out how many to remove.

If you can space a disk, create a dedicated VG for them in the short term, rather than filling up rootvg and making DR recovery a problem.



I hope that this helps,

Robin
Liverpool/Blackburn
UK