Kernel parameters 64 bit v. 32 bit

[MarkSyder]

Hi everybody.

I've been asked to compare the kernel parameters on two servers and correct any discrepancies. Unfortunately, one server is 64 bit and the other is 32 bit, so it's possible that some differences are appropriate and should not be corrected.

There are many parameters which are different - too many to post here. I would be grateful if someone could give me a list, even a partial list, of parameters which are supposed to be different between the two systems.

Mark Syder (like the drink but spelt different)

[T G Manikandan · Accepted solution]

I can give you a list what is remember

maxdsiz
maxtsiz
maxssiz

are parameters for 32 bit.For 64 bit you have maxdsiz_64 and their equ.

shmmax


take a look at
http://docs.hp.com/hpux/onlinedocs/939/KCParms/KCparams.OverviewAll.html

[Trond Haugen]

You could go back and ask if they rely want the kernel parameters the same as one is 32 and the other is 64 bit.
On the other hand you could assume the application is 32 bit. So it shouldn't matter. Then again there is the problem of knowing which system is correct...
And are the same SW and patches installed on both?
It seems to me you have been given a simple task. That turns out to be not so simple. Quite common I would say. :-)

Regards,
Trond

[Muthukumar_5]

Hai,

We can get the kenerl parameters with the kmtune or kctune command. Execute on the both machine and check difference.

On 11.23 using kctune
=========
maxdsiz_64bit 4396972765184 4396972765184 Immed
maxrsessiz_64bit 8388608 Default
maxssiz_64bit 0x40000000 0x40000000 Immed
maxtsiz_64bit 1073741824 Default Immed
nsysmap64 8400 Default
pa_maxssiz_32bit 83648512 Default
pa_maxssiz_64bit 536870912 Default


I have searched on the 64 bit machines. But i don't have 32 bit machine here. You can get the kernel parameter description with -d option.

Regards,
Muthukumar.

[MarkSyder]

Thanks Muthukumar.

I already know what the parameters are - it's just a case of knowing which are the correct ones.

I'm not awarding points to the other suggestions yet as I don't want to award a rabbit too soon - people might think it's resolved and not make any more suggestions. I have no objection to giving more than two rabbits!

Mark

[Trond Haugen]

well knowing which are the correct ones is the tricky part indeed.
If you have certain application running on both systems like Oracle, SAP etc. They will have some parameter values documented. If that is not the case you have to go by common sense or go for the biggest value.. Or a combination. But don't do the misstake of setting dbc_max_pct to 50 unless there is a good reason for it.
If there are certain parameters you are in bupt about, post them.

Regards,
Trond

[MarkSyder]

Thanks everybody - parameters set without any obvious problems (i.e. the server came back up!).

Trond - dbc_max_pct is already set to 50 on both servers. Why is this a bad thing?

Mark

[T G Manikandan]

The dbc_max_pct is the parameter which defines the buffer cache on the system.
This parameter gets enabled when your nbuf and bufpages are set to zero.

These parameters
dbc_max_pct
dbc_min_pct
defines the dynamic buffer cache on the
system

By default the value is 50% of the memory on the system.
If you are running machine with huge memory resources then you can bring them down to make the programs use the real memory for their purpose instead of locking them for buffer cache.

For ex, if your system runs with 2Gb ram you can bring down the dbc_max_pct to 20% which would equate to 400MB.

[Michael Tully]

The recommendation on buffer cache is somewhere between 300-500Mb. This is quite normal. Having this any higher hinders on both performance and the best use of the memory of your system.

dbc_max_pct 300-500Mb
dbc_min_pct no less than 200mb

[Michael Tully]

The recommendation on buffer cache is somewhere between 300-500Mb. This is quite normal. Having this any higher hinders on both performance and the best use of the memory of your system.

dbc_max_pct 300-500Mb
dbc_min_pct not to be less than 200mb

[MarkSyder]

Sorry Michael - I can't give you points for the same answer twice ;-). But thanks for the help anyway!

Mark