Some months ago, I wrote an article comparing EXT3, EXT4, XFS and BTRFS filesystem performances with a Fedora 14 x86_64 installation done on a Dell Latitude D620 laptop. While the results were quite interesting (especially to evaluate BTRFS performance), they were collected on a consumer machine (a laptop), with consumer-grade processor and HDD. So, the results do not necessarily translate to server world in a linear manner – a very good filesystem for a single 2.5'' HDD can be inadequate for a multi-disk server machine, and vice-versa.
Today, thank to the “Center for Research Computing” at University of Notre Dame, and especially to Paul Brenner, Serguei Fedorov and Rich Sudlow, I am able to present you some filesystem benchmark results collected on a quite powerful Dell R510 server, loaded with 12 x 2 TB SATA disk connected to a low-end, inexpensive PERC H200 controller. The article will focus on EXT4 vs XFS performance, as EXT3 can not grow bigger than 2 TB and BTRFS is way too young (and unproven) to be considered in the server world. I hope that these data can help you to chose the right filesystem for your workload.
While reading this article, please keep in mind that different usage patterns can favor different filesystems, so I don't pretend to elect the always-better, stronger FS on the world. I simply want to give you some numbers collected in various usage patterns, so that I can help you in the choice of the right filesystem for some common jobs. Please also consider that FS performances can vary dramatically between kernel releases; however, this behavior should be mitigated by the fact that RHEL 6.0 use very conservative, security-focused kernel updates.