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reduce available ram

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Operating Systems AIX reduce available ram
# 1  
Old 01-19-2007
reduce available ram
hello, we have a aix 5.2 server with 8GB of ram. is it possible, without actually removing the hardware, to have the O/S think it has only 4GB of ram? We would like to see how the handles and responds if it only had 4Gb instead of the 8GB. Any ideas or suggestions? Thanks

Looks like i found where this can be accomplished via smit by changing the 'amount of usable physical memory'. Does anyone have experience reducing this setting? Does it require reboot, etc? Thanks again
Last edited by zuessh; 01-19-2007 at 03:00 PM..
# 2  
Old 01-19-2007
I think it is intended for two purposes, one: as you mention, two: if the system detects a failure and deconfigures some memory - it allows you to check how much is remaining / available.
I'd not try to deconfigure it on the fly, I'd deconfigure in single user and reboot, then check it is still deconfigured. I don't think AIX has any way to recover from memory being stripped away from it if it were in use at the time it was deconfigured.
I can't find any thing on the IBM web site about it though.
# 3  
Old 01-20-2007
sure it can (dlpar), but I'm not sure if aix 5.2 can

never testet it this way, but if you want I can test it on monday with smitty
wondering which command smit uses

I can just test it on aix 5.3, don't have any AIX 5.2 playgrounds left
Last edited by funksen; 01-20-2007 at 06:36 AM..
# 4  
Old 01-20-2007
One needs two things to do it dynamically: AIX 5.3 and a LPAR.

Taking away or adding memory (without getting physical, that is ;-) ) is only possible in a LPAR machine, to do it without having to reboot is only possible with 5.3 onwards. Machines with older versions of the OS will have to be rebooted.

What you *can* do, though, is to create a RAMdisk with the "mkramdisk" command. This way you can take away arbitrary amounts of memory which the system doesn't have (effectively) available any more.

bakunin
# 5  
Old 01-20-2007
who mentioned lpar/dlpar! we are talking limiting memory from the smit sceens, chdev -l sys0 etc, etc.
remember systems without HMCs? even pre power4! they are still worth/ have the floor space....
# 6  
Old 01-21-2007
Quote:
Originally Posted by dukessd
I don't think AIX has any way to recover from memory being stripped away from it if it were in use at the time it was deconfigured.
thats simply not true and thats why I started with dlpar
# 7  
Old 01-21-2007
The question has been answered and the rules are being broken.

Thread closed.
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