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Good guidelines for selecting swap space?

Good guidelines for selecting swap space?

 
8 REPLIES
Charles McCary
Valued Contributor

Re: Good guidelines for selecting swap space?

Dan,

depends - how much memory do you have?

If you have a lot, then you probably want to investigate pseudo-swap (kernel parm) allows you to fool the system into thinking you have swap space for use, because if you have a lot of memory, then you shouldn't be swapping.

If you don't have a lot of memory, then you probably should go with the standard 2x memory.

tx,
C
Magdi KAMAL
Respected Contributor

Re: Good guidelines for selecting swap space?

Hi ,

If you got a production server with heavy transactions, then swap space would be 3 or 4 times the physical memory.

have a look at :

Essential System Administration.
O'Reilly
By Aeleen Frisch
Second edition
Page 315 and up.

Re: Good guidelines for selecting swap space?

I'm trying to develop guidelines that would cover many servers w/ many configs.

Re: Good guidelines for selecting swap space?

I really want to know where I can find the most indept explanation of swap (book or online)

Thanks,
Dan
Magdi KAMAL
Respected Contributor

Re: Good guidelines for selecting swap space?

Hi again,

When I upgrade to hp-ux 11.0, I did also a HW changes from K420 to L2000 class server.

I noticed that, for heavy oracle OLTP process, not enough space error messages are comming on all production systems ( 6 different production servers ).
The issue is, while some process is doing I/O, the schedular is putting them into swap and it try to electe other ones to fill into memory to be executed , but when there is a competition and the cpu speed is high then swap will not follow the semand for putting process lookuin for more I/Os. that's why by increasing the swap space by four times the physical mem, this problem had disappeared.

HTH.

Magdi
James R. Ferguson
Acclaimed Contributor

Re: Good guidelines for selecting swap space?

Hi Dan:

You might start here ("Managing Swap and Dump"):

http://docs.hp.com/hpux/onlinedocs/B2355-90742/B2355-90742.html

...JRF...
MANOJ SRIVASTAVA
Honored Contributor

Re: Good guidelines for selecting swap space?

Hi Dan

I agree with all others but the good place to start is to do it. Actually the swap is determind with the physical ram that is defined in the system . Genreally for systems mid range ones with RAm ranign form 4gb to 8-10 GB , it is better to have swap betwwnn 1-2 times the size of RAM and more the Physical the lesser the swap required . SO start with the same size ( I beleive you would be using 4-10GB RAM size ) and then go to tune using tools to display swapinfo etc .

Manoj Srivastava
Byron Myers
Trusted Contributor

Re: Good guidelines for selecting swap space?

Check out the memory management white paper on the system: /usr/share/doc/mem_mgt.txt. This
explains in detail how swap is used in HP-UX.
If you can focus your eyes far and straight enough ahead of yourself, you can see the back of your head.