Re: [Xen-users] iSCSi on Xen

[Alvin Starr <alvin@xxxxxxxxxx>]

Dan Cox wrote:

> I'm booting dom0 via PXE with iSCSI root and also the domUs use iSCSI 
> root. The latest syslinux is required for booting Xen kernels via PXE.
> The most stable iSCSI initiator I've found was Core-iSCSI (see 
> http://lwn.net/Articles/163608/) built against the Xen 3.0 release 
> kernel sources (don't forget ARCH=xen when building the module!). For 
> the target I'm using IET 
> (http://sourceforge.net/projects/iscsitarget/) built against the 
> latest FC4 kernel (2.6.14-1.1653). I've been running this for some 
> number of weeks and it's pretty solid. Performance is also good. In 
> theory, this also means I could migrate the guests around the network 
> transparently, but I haven't tested that yet. The only catch with the 
> software based iSCSI initiator is I had to roll a highly customized 
> initrd which logs into the iSCSI target(s) and in the case of dom0 
> brings up the bridge. I setup the initrd in such a way that I can pass 
> kernel parameters to tell domU/dom0 which targets to login to. Hope 
> that helps..
> Dan-
>
> Ian Pratt wrote:
>
> > > Has anyone been successful in installing and running iSCSI in
> > domain0?
> >  
I have had good and bad luck with all the initiators but Core-iSCSI and 
I have not yet gotten that one to work.
Currently I am having the most luck with open-iscsi It seems to give the 
best  in terms of being able to pick and choose what target I connect 
to. The one issue with open-iscsi is that it seems to use up lots of 
kernel memory.  If I connect more then 3 targets I run out of memory on 
my Dom0 that is only configured with 256M.
I have a 2.0.x version of xen running for nearly a year now with 
linux-iscsi but I was never able to recreate the config with more 
current versions of Xen.
I have my DomU's running using the drives as visable in the Dom0. My 
reason is that I believe that running through the block interface should 
be much faster than running over the bridging network connection.
The biggest issue with using the devices in Dom0 is making sure that the 
iscsi devices are available using predictable device names. To get this 
to work I have hacked the udev code to create the devices with a name 
that matches the target name as set up in iet.
I tried booting a Dom0 from an iscsi drive using grubs network boot 
capability but that did not work very well so I gave up doing that.  I 
have had some luck booting a regular system using syslinux but had to 
hack the initrd so badly that I just gave it up as being unsupportable.  
If the open-iscsi guys manage to get iscsid to be restartable it may be 
worth taking another look at that process again.

I have managed to migrate domains from my various xen servers so long as 
the iscsi devices were available with the same device names on each server.
--
Alvin Starr                   ||   voice: (416)585-9971
Interlink Connectivity        ||   fax:   (416)585-9974
alvin@xxxxxxxxxx              ||




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