The performance impact will most probably be very similar in both cases.
It doesn't matter if you are propagating a virtual block or net device,
the mechanism of transferring data between DomU and Dom0 is basically
the same - exchanging memory pages between those domains for all kinds
of I/O. So you can use either of them depending on which is better for
you from other viewpoints (like the ease of use).
Regards,
Daniel
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Marc Grimme
Sent: Wednesday, July 23, 2008 11:26 AM
To: Red Hat Enterprise Linux 5 (Tikanga) discussion mailing-list
Subject: Re: [rhelv5-list] guaranteed cpu power to VMs
On Wednesday 23 July 2008 11:08:48 Zavodsky, Daniel (GE Money) wrote:
> What exactly do you intend to do?
> If you want to compare using NFS directly in the guest via the network
> VS using NFS in Dom0 and propagating a simple file on it to a guest
> via the block layer, I'd strongly suggest you not do the latter. The
> performance penalty of such a setup would be considerably more than
> 20%, I'd say more like 40%. I haven't tried NFS but the penalty of
> using simple files on GFS/SAN and exporting them to a DomU is in that
range.
> In PV DomUs, network I/O performance is pretty good.
What we want to compare is not mapping any loopback device up to DomU
but we want to compare the performance of mounting a nfs-share in DomU
to using a raw blockdevices which resides on iSCSI in Dom0 and directly
map the /dev/sd?
to DomU. That second approach eliminates the IP-Stack in DomU and the
first approach uses it.
We would prefer NFS for the ease of use but are a little confused
because of performance considerations.
--
Gruss / Regards,
Marc Grimme
http://www.atix.de/ http://www.open-sharedroot.org/
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