Optimum amount of RAM for server

From: Lars Oberg (n-o-sp-am-lars_oberg_at_hotmail.com)
Date: 02/21/04 

Date: Sat, 21 Feb 2004 20:43:22 GMT

Hi,

I am trying to find out optimum amount of RAM for a Linux based application
server.

Details:
* RH Advanced Server 3.x (kernel 2.4.21, but with 2.5 and 2.6 features
added).
* Dual Xeon 2.8GHz 512 L2 Cache
* xGB RAM
* 300 GB RAID-5. 2GB CACHE on controller. (external SAN box via 2 GB fiber)
* Ext3 file system
* Cobol-based application (using ISAM database). Written in AcuCobol.
* About 150 concurrent users via telnet & ssh.
* Will also be Samba server for about 50 users (mostly light usage).

2GB of RAM meets and exceeds the requirements for the application (with 150
users), but I am considering 4GB of RAM instead.

My question is: With 4GB instead (2GB more of RAM available for file system
caching), am I likely to get a noticable performance increase? How about
added risk of dataloss due to more data not yet written to disk at the time
of a system crash?

Any advice on this would be appreciated.

Thanks in advance,

Lars

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