- Performance difference between SLES and RHEL
There is none per se. Both are Linux and other Free Software patched and closely watched by commercial providers. If there were great performance improvements Linus is the first person to examine them and adapt them in his kernel.
The difference between those commercial distributions and the free ones is the support for money. The fact that your IT people ask this question implies to me that they need support.
- Statistical data on what OS/distribution people use
Is of no use. The best OS/distribution is the one you master!
- Performance in 32 bit vs 64 bit Linux
There is an improvement, but it doesn't double! The figures in the net vary between 0 - 20%. See for example http://www.phoronix.com/scan.php?page=article&item=ubuntu_1204_3264
Still 64 bit is the state of the art, since a long time. Moving forward is not a bad idea, specially if you want to break the 4 GB barrier (RAM) without too much complications.
New server usually means new hardware. At the rate of the hardware becoming better and cheaper new hardware also means better performance. (OK, unless you suffocate them with bloat.)
Talking of hardware, make sure that your IT team mean hardware, not "images". If these Linuxes are inside a virtualization system, the entire discussion is going to be different one!
- General advice on Moodle performance
All the compulsory reading is in the introduction to this forum. There are wiki pages, links to past discussions and an advanced search facility. Please advice your IT staff to go through them carefully and also directly participate in this (Hardware and Performance) forum.
The reality is that with all the "tuning" you might get 10 - 20% improvement. But a single new release of Moodle can halve your output. See http://moodle.org/mod/forum/discuss.php?d=207390&parent=909633
. That definitely happened going from 1.9 to 2.x. It also happened going from 1.6 to 1.7. But during the long life time of 1.x experts got together and brought great improvements. Since about 1.9.9 the performance is almost as good as 1.6. Unfortunately that doesn't happen in 2.x, understandable in a way, who wants to polish a product which will be replaced in 6 months?
- About the current performance issues
Have they been discussed in this forum?