Can I suggest ZFS on Solaris/OpenSolaris? Real breeze to setup.
As for Linux, it has been a while but are there still two iscsi-target implementations? Has any one of them got into the mainline (Linux - not Redhat - although if Redhat will support one implementation I guess it does not really matter whether the mainline has it or not) kernel?
Serious performance issues wrt to ZFS under iSCSI on Solaris/OpenSolaris at the moment which require gobs of cash to fix. See rbourbon's post from this thread: http://opensolaris.org/jive/thread.jspa?threadID=111286&tstart=0
As for iSCSI on CentOS, I use iet versus tgt as the boxed instance leaves lots to be done manually. Iet is actively developed by a some bright people and is well tested/used and stable. I can assure iet works rock solid, I have it exporting block devices to ESXi, nix and windows without ever missing a beat.
Also, according to http://kbase.redhat.com/faq/docs/DOC-15154 tgt is still only a Technology Preview, so you wouldn't expect it to be complete yet.
jlc