LVM on top of software raid 1

dom0:~ # dd if=/dev/zero of=test_file bs=64k count=32k
32768+0 records in
32768+0 records out
2147483648 bytes (2.1 GB) copied, 28.7311 s, 74.7 MB/s

domU using 1024k mem, disk = phy:vg_xen/domu (same LV as tested above mounted in dom0)

Writing...
domU:~ # dd if=/dev/zero of=test_file bs=64k count=32k
32768+0 records in
32768+0 records out
2147483648 bytes (2.1 GB) copied, 215.65 s, 10.0 MB/s
Reading...
2147483648 bytes (2.1 GB) copied, 33.26 s, 64.6 MB/s

This test is on a quad-core xeon and have only one guest domain. Xen 3.3.1_18546_16-0.1
Tested on a dual quad-core with over 10 guests running and got the same results. Xen 3.2.1_16881_04-4.2