Sorry to not specify: it is a host related question, not about performance on guests machines ...
Honestly I wouldn't pick either of these because they both run a graphic interface by default and have a lot of extra stuff running that isn't necessary. If you want a fully supported distribution, perhaps Ubuntu server is a good choice since it is pretty tight on resources in that it doesn't run a lot of extras you don't need and doesn't install X by default. My servers currently run RHEL 4 and RHEL 5, my dev box runs Ubuntu 8.0.4 server and if it wasn't for the lab manager's policy, I would replace the server OS with Ubuntu. You can tighten down the RHEL or SUSE environment but I prefer not having to strip down a machine, I just want it to come that way.
As for performance they are going to be pretty similar really, and security they are both pretty good there as long as you keep up with patches. I am not aware of any real barrier difference between either of them for scalability unless you have specific specialized hardware.
So you think that free ESX 3.5i is not suitable?
Perhaps he is in the same position I am, using a Linux client machine which rules out ESXi at this point. Perhaps some day I will build a local Windows virtual machine just for doing ESXi but then I would have to beg for a license.
ESXi does look compelling though.
In the past 2 years I've been using, for 1.0x Server, the debian (first sarge, then etch) distro on 5 host servers (Prolaint DL360G4 , DL380G4 and DL320s) and found it pretty stable.
Also it allows me to have a very small foot print O.S. (around 450MB before installing VMware Server, around 1,1GB after installing it and all its needs, including the HP Insight Agents.
Lately I've been experimenting with the Centos 5.2 (64bit)because of some strange problems with 2 new Proliant DL580G5 for which the quite old agent packages that HP provides for Debian aren't good enough.
And I have to say I'm positively impressed, I can do a "stripped down install" which takes only 1,3 GB (200MB more than Debian).
You just deselect everything, even the "base packages", at the package selection stage (graphical install) and it comes out quite slim in comparison of the standard install; it doesn't even have the graphical desktop installed, which I think does make a difference (both in space and performance).
I had tried older Centos releases (3 and 4) but these didn't quite impress me as this latest one.
Just my opinion, I hope it helps!
The best host is the one you know the most about. If you're used to working with a Red Hat environment, such as previous RHEL or Fedora, then RHEL5 is probably the best way to go. If you're used to SuSE then go with SuSE.
Deep down, they're both the same so it's more a question as to what you know or what your site says you have to use.
I have to agree with the others. If it has to be between RHEL/CentOS 5 and SLES 10, I would recommend RHEL/CentOS. They are more standards compliant than SLES. SLES/Novel likes to do a few things their own way which can interfere with the normal operations/expections of packages and others.
If you are not locked into either of those, then I would also recommend Ubuntu Server 8.04. I have been using it since release and I am very happy with its current stability and performance. Also.. I prefer debian packaging over Redhats which gives me a good deal of bias as well.
I've tried Ubuntu server 8.04 and managed to install VmWare Server 1.06 on it with no insormountable problems.
Also I too prefer debian packaging over redhat's , but alas, the insight management agent packages from HP (the ones for debian etch) just don't want to run on Ubuntu 8.04...
I mean, they seem to install but there's always some library missing (and HP doesn't update the packages!).
I guess it's because of the glibc that in ubuntu (and in debian lenny too) has been updated to 2.4 or some other similar fundamental system library.
Have a nice evening,
Slackware 12.x @ runlevel 3 (w/o gui). There is nothing like on RHEL, SLES (updatedb, cronjobs, ...) which takes unneeded cpu cycles on the host and starts unneeded services.