I am rerunning numbers for dom0/domU on vnodes to be a bit clearer.

The system is a 3400 Mhz P4, Intel 915 chipset motherboard with 4 GB
DDR2 RAM.
There are 2 SATA drives:
wd0: drive supports 16-sector PIO transfers, LBA48 addressing
wd0: 372 GB, 775221 cyl, 16 head, 63 sec, 512 bytes/sect x 781422768 sectors
wd0: 32-bit data port
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133)
wd0(piixide1:0:0): using PIO mode 4, Ultra-DMA mode 6 (Ultra/133) (using DMA)

The dom0s filesystems are all in RAID-1 using raidframe, and ffs.
I might have made the large filesystem ffsv2, but I don't remember.

dom0 is pretty recent NetBSD current.
The domU I use for this example has the same NetBSD current code.

All times are from dd if=foo of=/dev/null bs=256k, waiting at least 10-20s

dom0:
rwd0d		70 MB/s
rraid0d		66 MB/s
/n0/xen/foo-wd0 53 MB/s (for the first 10s or so)
		47 MB/s (over a longer time)

domU:
/dev/xbd0d	52 MB/s
                50.5 MB/s (85s for entire 4GB disk)


While it would be nice to have 70 MB/s in domU, I don't view the
current situation as a huge problem - my domU is as fast as many of my
older comptuers.  I have a dom0 with several domUs now, and heading
for 6-8.  The ability to change virtual disk sizes via files rather
than raw partitions (not to mention running out of 16 bsd partitions)
seems worth the slowdown.

It does seem that the Xen disk overhead is very low.

-- 
        Greg Troxel <gdt@ir.bbn.com>