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semi-n00b here. I'm setting up a server that will have Ubuntu 8.04 LTS with a LAMP setup. The system is dual Opteron 248s with 4GB memory.

I had a few questions about settings in the bios:

  1. Will turning off (disable) some of the hardware from bios free up memory for the OS? So disabling the USB Host Controller, serial/parallel ports, floppy disk controller, pci device slots, etc.

  2. I have a setting for "CPU0,CPU1 Link Tx Speed" with option for 800MHz or 1GHz and "CPU0, GOLEM0 Link Tx Speed" with option for 600MHz or 800MHz. Should these be set to the highest settings? Or, how do I consider what these should be set at.

  3. I have a setting for "4GB Memory Hole Adjust" Auto or Manual. It is currently set to Auto but if I set it to Manual I can choose the "Memory Hole Size". I assume this is for the amount of memory set aside for the hardware. Should this be adjusted? But also it leads to my next question...

  4. I am still undecided on 64bit or 32bit OS. If I upgrade to 8GB I will definitely go with 64bit. But with 4GB at the moment and just a vanilla 32bit ubuntu-server installed, the 'free' command shows: Memory: 4090732 (total), 42272 (used), 4048460 (free)
    Swap: 4803392, 0, 4803392
    Does this mean the OS is getting access to nearly the full 4GB of memory? Also, with 4GB memory, will 64bit give me improvement in performance vs 32bit for a server hosting the full LAMP stack? And what about if I migrate MySQL off to its own dedicated server?

  5. My other machine is dual Athlon MPs with 2GB memory, so 32bit. How do you recommend I use these 2 servers (for best performance) that are hosting a couple of my own sites all on LAMP setups. Do I put MySQL on its own machine, or what do you recommend. I have ecommerce sites as well as a social network type site with photo uploads and some GD processing going on with php.

Thanks and sorry for so many questions.

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up vote 4 down vote accepted

First off, it sounds like you're leaning towards premature optimization with your question here. Machines are pretty fast. You need very significant load on any reasonably designed, normal-ish website (in the many hits per second range) before you're going to hit the limits of your dual Opteron system.

(1) No, or at least not noticeably so. It may free up IRQs, etc., but you probably don't need to worry.

(2, 3) Don't play with BIOS settings if you have no idea what they do. (For 2, the proper setting, I believe, depends on hardware, and hopefully your system builder knew what he was doing.)

(4) Due to the additional registers you get in 64 bit mode, 64 bit is almost always a better choice. Also, while the system can see 4GB (or more) RAM, an individual app — say, MySQL — will be limited to 1.5–3GiB depending on kernel config. And you definitely don't want to reinstall if you decide you want a bigger MySQL query cache and add RAM.

(5) This is hard to say without knowing the performance characteristics of your sites. First, if it doesn't matter (your performance requirements are not very high, determined by measurement) I suggest saving electricity and turning off the second machine. If you have the load, then often splitting MySQL to its own machine helps, and I'd use the 64-bit box for MySQL because databases, in general, love RAM.

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+1 Perfect answer – David Pashley Jun 5 '09 at 7:35

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