Memory limit on iSeries

[Former Member]

hi,

In note 808607, there is a line:

Extended Memory

In the standard system, the maximum size of the available IBM memory is restricted to 64 GB and this corresponds to a value of 66536 for em/initial_size_MB.

What have people done when they reach this limit of extended memory size of 64GB?

I'm currently running an p570 central system and our EM is currently at 40GB. We expect to hit 64GB before all our rollouts are completed.

Do we need to run additional application servers? Or can we increase physical memory on the box and run multiple instances using up to 64GB?

Any advice, please.

Thanks, Andy.

[Former Member · Accepted solution]

Hello Andy,

You said "p570 central system". Are you running SAP on AIX or iSeries?

I don't think 64GB is the limitation of Extended Memory for SAP on iSeries. In same Note, it states that "Each SAP memory type (roll memory, extended memory, heap memory, paging memory) is ultimately based on teraspace on OS400/PASE. This means that 1 terabyte is available for the address space of the SAP System."

You could test it on DEV/QAS/SBX SAP system. Even the physical memory is not that big, when SAP starts, only virtual memory is allocated. And you can always switch it back easily.

Best regards,

Victor

[Former Member · Accepted solution]

Hi Victor, Sorry, I meant i570 not p570... I'm doing a lot of work with AIX too, and I guess I always imagined that they are really the same box with different firmware.

The problem we have had is that we had em/initial_size_mb set to 32GB until recently, and we started getting 'Em exhausted' errors which lead me to believe that I had to increase em/initial_size_mb. The problems went away, and EM size increased above 32GB.

Then when I found this apparent limitation it worried me that I would have to change the structure of the system setup significantly (for example add new dialog instances) if I reached 64GB.

Thanks, Andy.

[Former Member · Accepted solution]

Hi Andy,

with your 40GB you are even nearer to the limit than you think ;-(

You need to increase the following parameter as well:

as4/MAXSHR64

=> Max. Shared Memory Size for EM (in 256 MB Segments)

(needs current R3INLPGM patch)

e.g. note 808607

=> you could set this to e.g. 800 for 200 GB em - even when you do not need that ...

Then you can increase em/initial_size_MB - do not forget to increase em/blocksize_KB to 8192 when EM becomes larger than 64 GB ... (you do have "only" 16384 slots there)

Hope this helps,

Volker Gueldenpfennig, consolut international ag

http://www.consolut.de - http://www.4soi.de - http://www.easymarketplace.de

[Former Member · Accepted solution]

Thanks Volker, I must admit I didn't quite understand note 808607's line:

"If you require more memory in PRIV mode, you must insert a line of the type

as4/MAXSHR64 = 400

in the SAP instance profile."

I don't think I want more memory in PRIV mode.

However, I am sure you are right and I'm relieved to know that I am in fact not constrained to 64GB.

So, I believe I should go for:

as4/MAXSHR64 = 800 (allow max 200GB)

em/blocksize_KB = 8192

em/initial_size_MB=65536 (for example)

to take me up to the full 64GB.

I don't need to do this yet, but at least now I am prepared and can prove this in QA.

Many thanks for the advice, I clearly need to re-read and digest note 808607 - it has not been at all clear to me. Perhaps the German version is clearer.

Andy.

[Former Member · Accepted solution]

Hi Andy,

I would go for:

as4/MAXSHR64 = 800 (allow max 200GB)

em/blocksize_KB = 4096

em/initial_size_MB=60000

As soon as this above becomes an issue, I would go for:

as4/MAXSHR64 = 800 (allow max 200GB)

em/blocksize_KB = 8192

em/initial_size_MB=120

Why ? Because the higher Blocksize increase the overhead as the smallest piece of memory is then 8MB => the EM untilization will really climb up when changing this parameter .... => you want to double in order to be on the safe site and then you can reduce when you do have experience with the new blocksize

Hope this helps,

Volker Gueldenpfennig, consolut international ag

http://www.consolut.de - http://www.4soi.de - http://www.easymarketplace.de

[Former Member · Accepted solution]

Thanks Volker!

I will try this in QA and the move forwards as soon as we approach running out of EM again.

I hope you can do another iSeries performance workshop soon!

Cheers, Andy.