James is probably correct. CMS is aware enough of its environment to ask CP
how much storage it has, thus never has to touch each of its pages (as some
operating systems do). It's also better behaved (for a virtual storage
environment) in releasing pages it isn't using.
For a CMS-intensive environment, the first factor in the calculation is
probably better "sum of the working sets of the logged on users," a slightly
more difficult value to obtain than the sum of defined storage sizes.
You could also work it backwards. If your DASD page space is under 50% full
at peak (the usual target value), you could reduce the amount of space
defined until you get close to that. However, be sure to allow for workload
growth; don't trim too close to the 50% full mark.
Marty
____________________
Martin Zimelis
Principal
maz/Consultancy
________________________________
From: The IBM z/VM Operating System [mailto:[EMAIL PROTECTED]
On Behalf Of Huegel, Thomas
Sent: Wednesday, December 12, 2007 10:19 AM
To: IBMVM@LISTSERV.UARK.EDU
Subject: Performance ? How much page area to allocate?
IBM publishes a formula for calculating how much page space to
allocate.
The formula is something like this: (Total amount of logged on user
storage - amount of REAL memory) x 2 = the amount of storage to map to DASD.
When I do this calculation I come up with a requirement of 10 3390
mod3 for my page space.
I only have 2 3390 mod3's for page and I don't seem to be having any
problems.
The question is 'am I missing something'?
My page rate is < 2/sec.
The only thing I ever see is occasionally LINUX will slow down for a
second or two.
Any thoughts or comments would be appreciated.
Thanks
