Hi everybody. I have an older RHEL server that I'm looking to replace with a new server running CentOS. Essentially it's a samba server and also runs lamppp for a very small website.

I'm trying to figure out how much RAM I need in the replacement server, so figured I should figure out how much it's using now, but have no idea how to do this really. Any suggestions?

I only have an anti-answer, not an answer. But it is still something you should understand.

Unless the old system has a severely insufficient amount of ram, it is using most of its ram for file caching (it is a Samba server). More or less ram probably just means more or less file caching, meaning less or more disk I/O.

I expect you can somehow measure the rate of disk reads vs. hits in the file cache. But you want to know how much better that would be with more ram. I have no idea how to measure that.

A commonly misunderstood place for the info on your initial question is the swap usage. I expect your system has some swap space configured and some of it is in use. It is a common misconception that any use of swap space is bad and indicates insufficient ram. That is not correct. A server that has been up a long time should have some swap space used. The amount of swap used won't vary much across the whole range of moderately insufficient ram through significantly excessive ram. If you have significantly insufficient ram then more swap will be used. If you have wildly excessive ram, no swap will be used. (If you don't enable swap then no swap will be used, which is a bad idea).

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Hi John, thanks for the reply. I do have swap on my server. Guess I'm just wondering if I should stick with what my current server is, or how much I should increase it since i'm moving to a new version of OS, etc. I mean, it is working now, but still figured i'd ask.

Yeah, I wasn't even going to take into account swap, since swap is going to swap anyway :-)

Any form of SAR: sar, Atop, Dstat, Collectl (hey Mark! ;-p) etc, etc reporting over time.

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Thanks. I will check them out. Any of them have easier to understand/simpler output than the others that you would suggest?

Check them out, then ask?

I did look at them.

sar makes my head spin so gotta reread when I get time later.
atop I think I need to leave running from the console for a while to see if it ever hits critical levels?
dstat also looks like a let it run and collect data tool, then I have to open the output in excel it sounds like
collect I didn't get to finish reading the man page for but will later.

Yes, that's the idea: let them collect details for some time. And because they all can output plain text you're basically free to do with it what you want.

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OK, thanks.