topic Re: swap area in Operating System - HP-UX

swap area

Domenico_5 — Wed, 17 Apr 2002 12:08:02 GMT

Hi to all

I have this scenario, an L2000 server with 2 36Gb disks. It is connect to a VA7100.

I must create a 40Gb Swap. The question is:

Is correct create 20Gb on primary disk and 20Gb on VA? VA have raid5 it's a problem for swap?
It's supported???

tnx to all

Re: swap area

James R. Ferguson — Wed, 17 Apr 2002 12:19:14 GMT

Hi:

You are not going to be able to do this, but not for the reason you asked. The maximum swap space allowed is 34GB:

http://docs.hp.com/hpux/onlinedocs/os/KCparam.MaxSwapChunks.html

Regards!

...JRF...

Re: swap area

Helen French — Wed, 17 Apr 2002 12:40:59 GMT

Hi,

It is possible to do that. I think JRF has pointed a littlebit old document. 34GB was the limit earlier. Now the system imposed maximum swap space limit is 1 terabytes ! (= 1.09 trillion bytes.

# sam -> kernel configuration -> configurable parameters -> select 'maxswapchunks' and press f1 for help.

There is no problem with defining the swap space in the disks and in the disk array. RIAD-5 will give redundancy too. You can define these primary and secondary swap space with SAM. It will adjust the kernel parameters too.

HTH,
Shiju

Re: swap area

James R. Ferguson — Wed, 17 Apr 2002 13:15:34 GMT

Hi Domenico & Shiju:

Thanks Shiju, I agree! I quoted for 11.0 as referenced, but had not looked fully at 11i documentation. So, depending on Domenico's environment, he may indeed exceed 34GB. In fact, a very good insight into swap space, including the parameters 'maxswapchunks' and 'swchunk', can be found in the 11i kernel documentation:

http://docs.hp.com/hpux/onlinedocs/TKP-90202/TKP-90202.html

Regards!

Re: swap area

Bill Hassell — Wed, 17 Apr 2002 13:22:53 GMT

36 Gb of swap? Wow, you must be planning on running thousands of users and 10's of thousands of processes. There are some 3rd party recommendations about swap space that are very badly out of date, something like RAM*10 or similar. Unless you will be running processes that consume 20 Gbytes more space than you have available RAM, I would not waste the disk space on an unused resource. The correct amount of swap is calculated by seeing how many of your processes do not fit into memory at the same time. For large memory systems (ie, 8Gb and higher), this may be: none so swap can be a couple of Gb. If you have 2Gb of processes (and memory mapped file space--if used) that can't fit into RAM, then I would make sure there is about 3-5Gb of swap.

Re: swap area

Domenico_5 — Wed, 17 Apr 2002 13:32:12 GMT

hi bill

I have the same idea, but sap have asked me this and I don't know why.

Re: swap area

Helen French — Wed, 17 Apr 2002 13:35:50 GMT

Hi JRF:

I am glad that I could point out this =)). Infact I was trying to post the reply first, but could see your reference of 34GB. Then it took a while for me to check and clarify this limitation ( 1 terabytes ), as we all know you rarely make mistakes ! The limitation is for 11.0 as well as 11.i.

Domenic, Bill has a very good point here. I would suggest you to check the swap utilization first, then increase if needed.

HTH,
Shiju

Re: swap area

Clemens van Everdingen — Wed, 17 Apr 2002 17:48:26 GMT

Hi,

I have heard about these crazy swap space sizes recommended by SAP as well.

I am not sure of teh reason for this, but I will be able to find out more when I am in my office tomorrow.

I believe it has to do with the number of instances you are running.

Did you have specific problems why they asked you to increase the swap space ?

If you like to know more, let us know !

Regards,
Clemens

Re: swap area

Dave Wherry — Wed, 17 Apr 2002 21:11:21 GMT

I believe earlier versions of SAP such as 3.1h did a check of the swap space during startup. We had application servers that would not start unless there was at least 3.5 times RAM of swap available.
The irony of it was, those boxes had enough RAM that they never swapped. It was just pre-allocating swap.