[Xen-users] NFS DomU Client Performance

["HAWKER, Dan" <dan.hawker@xxxxxxxxxxxxxxxx>]

Hi All,

Quick question regarding NFS performance and Xen.

Have a series of Xen boxes running Xen 3.0.2 on FC5 with a stock FC5 Xen0/U
2.6.16 kernel. All things generally are great.

Was planning to deploy a couple of VMs for a couple of our software
developers so that they can test new software in relative safety, however I
am experiencing some poor performance issues with NFS.

NFSServer1 - Standard FC5 box (ie no Xen)
NFSServer2 - Xen based DomU FC5 box (exactly the same as above but runs as a
DomU)

DevClient1 - Standard FC5 box
DevClient2 - Xen DomU FC5 box

Basically, if I mount a NFS share from either NFSServers on DevClient2 it
takes a while to mount, but will eventually mount fine. If however I try to
mount a share on DevClient1 it mounts instantaneously. I have tested this on
a number of DomU boxes I have around for other services (LDAP/DNS/etc) with
similar results. Equally if I mount shares from a number of non-Xen boxes it
is again instantaneous.

Now I was expecting some overhead with Xen networking (as you'd expect) but
this is a bit more that I was expecting. From my initial testing (admittedly
probably a little rough), a simple *mount nfsserver1:/mountpoint
/mnt/mountpoint* sits there for a good 90 seconds (although the end result
is it does mount), whereas a non Xen client mounts in under a second.

It doesn't seem to make any difference whether the NFSServer is a Xen or
non-Xen environment, the limiting factor always seems to be the Xen Client.

Initially I thought this maybe DNS issues, but this doesn't seem to be the
case. I have digged around and all is normal with correct results from any
machine. 

Any suggestions, is this a known problem, etc, etc??

TIA

Dan
--

Dan Hawker
Linux System Administrator
EADS Astrium

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