RE: [Xen-users] SMP, Win 2k3 R2 Server, and GPLPV

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> 
> Mike,
> I currently use Xen 3.2.0 from SLES 10 SP2.  I have several of these
> machines, backed by an FC SAN.  My domUs all use file:-based access
(loop
> devices, essentially) to access their disks.  One of those systems
(Dell
> PE1950, 2 x Quad-Core Xeon 2.66 Ghz, 16GB of RAM) runs 20-25 Windows
XP
> SP3-based domUs with no performance issues at all.  At initial boot,
> sometimes there's a good deal of CPU usage on dom0, but that only
lasts
> for a little while, then things settle down.  My domUs are (mostly)
single
> vCPU with 384MB of RAM assigned to each domU.  I have one that has 1GB
of
> RAM and one that has two vCPUs.
> 
> On another machine (identical hardware), I also have a Windows Server
2003
> domU running, with 2.5GB of RAM assigned and 2 vCPUs.  All of the XP
domUs
> and the Server 2k3 domU use the GPL PV drivers.  I'll have to figure
out
> which version - I don't remember the exact release off the top of my
head.
> 
> I'm not sure what the performance of tap:aio is supposed to be, but
loop
> (file) works fine for me.  I can imagine that the software RAID would
have
> a negative impact on performance.  Since I'm using SAN-backed volumes
for
> storing my domU files, I'm not running any software RAID inside the
domUs
> or on the dom0s, so that's not an issue for me.
> 

I've just migrated from a low end HP raid controller (E200) running
RAID1 to software RAID1. My benchmark was doing backup exec restores
from a physical machine onto a DomU (connected via gigabit Ethernet).
Some approximate data points were:

E200+file:+GPLPV = 320MB/min but the Dom0 would freeze after about 8GB
restored and the restore would fail

E200+tap:aio+GPLPV = 12MB/min. This would probably run to completion but
I wasn't going to wait

E200+file:+qemu = 270MB/min and restored to completion

SW RAID+tap:aio+GPLPV = 620MB/min (and everything remains responsive the
entire time)

Obviously something was wrong somewhere for the E200 to perform that
badly, but don't underestimate the performance of software raid,
especially RAID1 (I wouldn't recommend RAID[56] to anyone who cares
about performance, be it hardware or software RAID).

James

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