My requirements are PHP and MySQL running stable on CentOS and dual Opterons.
The question is whether to install the 64-bit or 32-bit version of CentOS. I wanted to use a control panel such as Directadmin, but the more I hear about 64-bit, the more I hear problems, especially with PHP and MySQL.
Should I go the 32-bit route, or am I wasting my system resources this way? What do most of you guys do?
If you want stability, for a production server for example, then stick to what is known to work - 32bit. If you want to play, or otherwise experiment with the latest stuff to see how well it works, then go 64-bit.
For a production server, why are you even entertaining thoughts of 64bit if you think it won't be as reliable as you'd like.
I would rather have an old 32-bit system that just worked than any amount of performance increase from a 64-bit system that got me out of bed in the middle of the night to fix problems with it.
The 64-bit version of CentOS is very reliable and used in a fair number of places, although I would recommend RHEL or SLES (SuSE Linux Enterprise Server) if you can afford it simply because you get the support contract with it.
Lets remember that 64-bit Linux is NOT a new thing, it's been running (and I've found it to be very stable) on a range of 64-bit architectures such as Alpha, UltraSparc, Power5, PA-RISC and Itanium for a number of years.. This is tried and tested technology which is backed by major corporations such as Intel, HP, Oracle, IBM etc.
As for performance it's very likely that with MySQL running in native 64-bit mode you will see a noticable performance increase compared to 32-bit mode (although largely due to the greater number of registers available to the compiler).