AIX

Dear All,

During installation of SAP, it shows like below :

Code:

Condition : Swap Size
Result Code : Condition not met
Severity : MEDIUM
Message : For the selected services at least 74228 MB swap space are recommended. Current value: 65536 MB. (Updated 2005-06-24)

I am working on AIX OS.

Output of "lsps -a" is :

Code:

# lsps -a
Page Space      Physical Volume   Volume Group Size %Used Active  Auto  Type Chk
sum
hd6             hdisk0            rootvg       65536MB     1   yes   yes    lv

0

Before it's size is of 40128MB, i extended it up to above value.
But from that, i cant extended it as per the requirement mentioned above.

If i try to extend it shows as :

Code:

# extendlv hd6 1G
0516-787 extendlv: Maximum allocation for logical volume hd6
        is 512.

Please suggest me, How to proceed further, or is there any other way.

Waiting for your replies,
Thanks in advance,

Regards
Vamsi.

try

Code:

 
chlv -x <no of lps> < lvname>

Hi xoops,

Can you please let me know, exactly what the command does?

Regards
Vamsi.

First off: SAP has a long history of "recommending" certain amounts of swap. You can safely ignore these recommendations as they are complete nonsense.

If your system has some memory shortage it will start swapping. Once it does so you need the swap space and once this swap space it exhausted (or nearly exhausted) your system will start killing processes - so far, so common. But long before your swap space is exhausted you will have a severe performance degradation and you customers will be all over you to get the system back to speed - so far, so common either.

But as long as your system doesn't have a memory shortage you don't need swap space - *any* swap space! This means, while it is a god idea to have some swap space as a contingency you don't *need* it (under "normal" circumstances, which means there is indeed enough memory) at all.

SAP now recommends to configure swap space based on a simple formula: your current amount of memory times some factor (if i remember correctly it was 2). Would you increase your memory, which would make swapping even less probable their recommended amount would even increase, while there is a simple way to meet their requirements: reduce the memory of the system, which will make swapping occur more often, but SAP will recommend a smaller swap space for this (in fact now ill-tuned) system!

You see, their recommendation is simply bovine manure.

Historically the AIX kernel used an "early swap allocation" and allocated swap space for every started program, so the recommendation of SAP made - least some - sense back then. Since the days of AIX 5 (or was it with 5.1? A lot of years back for sure!) IBM changed that and now AIX uses late swap allocation. Since this change the recommendation makes no sense at all.


Regarding your error message: There is a parameter for each LV, which shows the maximum numbers of LPs that can be assigned to it. The command xoops told you will increase this maximum for the LV which holds your swap space. You can also do it using SMIT by issuing

Code:

smitty chlv

and follow the menus on screen.

I hope this helps.

bakunin

Moderator's Comments:

BTW.: i have changed the threads title to "recommended".

While I totally agree with literally every word Bakunin said... if you start paging you do not need bigger paging spaces you need more memory A healthy AIX box with sufficient physical does not page (at least not after AIX 5.3 when lru_file_repage has been switched off as it should be).

I would like to add a few things.

If you start swapping, one of your major problems will not be the size of your paging space but how fast you can access it. So more smaller swapspaces of same size on different 'idle' disks make much more sense than one big slow swap area.

Apart from this, AIX cannot manage swapspaces bigger 34 GB. So if you want to go really with big paging areas, than create at least 2 of them - same size but smaller 34 GB.

Regarding SAP - actually their recommendation (and similar as well for oracle and sybase) on current AIX boxes with sufficient memory is
up to 4 GB memory - 2x size of memory + 256 MB
4 - 16 GB memory - size of memory
17+ GB - 1/2 size of memory + 4 GB

Regards
zxmaus

Wait, what? Linux gets so much flap about its OOM-killer and other UNIX has them too?

on AIX its a tunable where you say kill processes and survive or die and reboot