Re: [Xen-users] iSCSI initiator on Dom0, exported to DomU via xvd, Disk IO Drops in Half...

["Barry van Someren" <barry@xxxxxxxxxxxxxxxx>]

Hi there,

I've used Citrix Xenserver 5.0 before this and never experienced this problem.
I did however store the entire VM on the LUN instead of mounting it to the VM.

Maybe you can trying doing that and seeing if it makes a big difference?

Regards,

Barry

(Failed to send this to the entire list, so sending again, sorry)

On Tue, Jan 13, 2009 at 11:48 PM, Christopher Chen <muffaleta@xxxxxxxxx> wrote:
> Hi there!
>
> I've been wrestling with an issue for a little bit now--
>
> In my test environment, I have tgtd running on a Centos 5.2 box, with
> a raid 10 array backing it.
>
> The initiators are also Centos 5.2 boxes running Xen 3.0.3 userland
> with a Xen 3.1.2/Linux 2.6.18 kernel (as from repos).
>
> Bonnie++ on the Dom0 shows about 110MB/sec writes, and 45MB/sec reads.
>
> I've attached the iSCSI LUN to the DomU as a virtual block device, and
> I'm seeing 47MB/sec writes, and 39MB/sec reads.
>
> I've tried a few things, like running against a local disk, and
> suprisingly, writes on the DomU are faster than the Dom0--can I assume
> the writes are buffered by the Dom0.
>
> I'm going to give a shot doing the initialization from the DomU (just
> for kicks...)...and wow! 129MB/sec writes, 49MB/sec reads.
>
> This is all with bonnie++ -d /mnt -f -u root:root
>
> Anyone seen this, or have any ideas?
>
> Is any additional latency provided by the xen virtual block device
> causing a degradation in TCP performance (i.e. a window size or
> delayed ACK problem) or is the buffering also causing pain? I'm going
> to keep looking, but I thought I'd ask all of you.
>
> Cheers
>
> cc
>
> --
> Chris Chen <muffaleta@xxxxxxxxx>
> "I want the kind of six pack you can't drink."
> -- Micah
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users
>



-- 
Barry van Someren
---------------------------------------
Email: barry@xxxxxxxxxxxxxxx
Email: goltharnl@xxxxxxxxx
Linked in: http://www.linkedin.com/in/barryvansomeren

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