With LVMs you'd of course lose the flexibility of file-backed targets and the ability to do sparse files are you're intending..
dd if=/dev/zero of=iqn.2009-12.com.mydomain:storage.disk01.foo.foo bs=1 count=0 seek=16G
LVM was my first option and performance it is very very good with iSCSI, but backup and restore it is a problem with LVM. For these reason I need to use large files on this server...
I actually prefer backing up LVMs.. I use the snapshot feature which means I can backup a live volume. Works well.