RE: [Xen-users] NFS DomU Client Performance

Petersson, Mats
Wed, 23 Aug 2006 13:07:55 -0000

> -----Original Message-----
> From: xen-users-bounces@lists.xensource.com
> [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of
> HAWKER, Dan
> Sent: 23 August 2006 13:28
> To: xen-users@lists.xensource.com
> Subject: [Xen-users] NFS DomU Client Performance
>
>
>
> 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??

I have no suggestions, but I would like to know if you''ve tried to see
what is different between the two ways to connect by using for example
tcpdump to see what the network traffic between the two machines look
like in the different cases.

Also, what''s the configuration of your NFS server machine: What type of
processor, number of cores, amount of memory (Dom0 and DomU memory setup
in the Xen case).

It may be that with this information, the problem can be solved quite
easile [but it may also be that it can''t - I haven''t played
with any of
the above parts, so I don''t know...]

--
Mats
>
> TIA
>
> Dan
> --
>
> Dan Hawker
> Linux System Administrator
> EADS Astrium
>
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