Why this difference

[Richard Perez]

I have two Itaniums: a 2600 and a 4640. The rx2600 uses just 500 MB after boot (obtained as Physical minus Available on dmesg: 1 GB - 512 MB) but the 4640 uses 1.2 GB (10 GB - 8.8 MB)

Why the difference?

[Dave Hutton]

Kernel Params exactly the same?
dbc_min_pct and dbc_max_pc?

[Pete Randall]

Buffer cache? What are the dbc_max/min settings on the two machines?


Pete

[Geoff Wild]

Could be one of several kernel parms...like dbc_max_pct....you are comparing a 10GB
server to a 1GB server...

Probably have different swap sizes as well...

Are both servers running exactly the same apps after boot is started? or are some things turned off (samba for example) on the 1GB box but turned on the 10 GB box?

Rgds...Geoff

[Richard Perez]

great hints, thanks:
-both systems have 5 as dbc_min, but the 2600 has only 1 GB RAM (then 50 MB min buffer cache) while the 4640 has 10 GB RAM (then 500 MB buffer)
-The 4640 uses 500-700 MB more at boot, grossly coinciding with the differences between buffer cache.

Do you think a 3 dbc_min and 6 dbc_max will be appropriate for a 10 GB RAM server running Oracle on raw dvices?

[Richard Perez]

Geoff
different swap sizes could effect the available RAM memory?

[Pete Randall]

Richard,

Normal recommendations specify 300 to 400 MB, so 3% seems appropriate. If you have Glance installed it should be easy to measure how well this is working.


Pete

[Geoff Wild]

You can also hard set the bufer cache - as pct varies...if you want them to be exactly the same...

Take a look at:


http://h21007.www2.hp.com/dspp/files/unprotected/devresource/Docs/TechPapers/UXPerfCookBook.pdf

Rgds...Geoff

[Richard Perez]

Thanks everyone.

[Richard Perez]

Thanks