Re: [Xen-users] mount DomU root fs via. NFS

[Adam Goryachev <mailinglists@xxxxxxxxxxxxxxxxxxxxxx>]

On 31/07/14 08:02, Gordan Bobic wrote:
> If you want to run your dom0 on NFS root, there is nothing stopping 
> you from making a custom initrd that will initialize your bridge 
> device appropriately. The kernel and initrd get fetched by PXE via 
> TFTP before the kernel even boots, so you just need to make sure your 
> initrd brings with it everything you need to set up the bridge and 
> initialize it before switchroot.
> Extract the initrd you are using and look at the /init file. It should 
> be just a simple shell script. You can edit it to do what you want, 
> repack the initrd, upload it back to the tftp server, and you should 
> be good to go.
> Gordan
Just to confirm that this is possible, I'm running debian squeeze in 
this exact way, dom0 is NFS root, and domU are all also NFS root. In 
fact, the dom0 doesn't even have any HDD at all, just boot via PXE.
The main issue was to disable xen from messing with the network at 
bootup, the easiest way to do this was to create the xenbr0 bridge in 
the initrd. I thought there was a lot of work done to make this easier 
in more recent versions of xen (ie, xen doesn't mess with the 
bridge/interface config, the OS deals with that), but I haven't upgraded 
to current debian stable yet. One option might be to use one ethernet 
device for PXE/NFS, and a second ethernet device for your xenbr and the 
domU's, this is a nice solution to keep "user" traffic separate from 
your "management/storage" LAN.
Ultimately, I'd suggest having at least three ethernet interfaces, one 
for storage, one for management, and one for the "user" traffic, though 
this will depend on your traffic load and requirements, and 
infrastructure options.
If you need additional assistance, let me know, and I can send you some 
of my scripts/etc that I used to create the initrd.
Regards,
Adam

> On 07/30/2014 06:03 PM, Jeenu Viswambharan wrote:
> > Hi,
> >
> > I've Dom0 running on Vexpress with the file system mounted via. NFS. I'm
> > also trying to get the DomU file system mounted via. NFS.
> >
> > Because the Dom0 file system is already mounted via. NFS, I believe I
> > can't use bridging because that'd involve taking the eth0 interface
> > down. A quick search suggested that bringing eth0 down will freeze the
> > system. I therefore instead chose to go with NAT instead.
> >
> >  From [1], all that's to be done in Dom0 is to
> >
> >    echo 1 > /proc/sys/net/ipv4/ip_forward
> >
> > And I've in my guest configuration:
> >
> >    ...
> >    vif = [ "script=vif-nat,ip=192.168.1.1" ]
> >    extra = "... root=/dev/nfs nfsroot=my.ip.add.ress:/path/to/root ..."
> >    ...
> >
> > What I see is the guest waits to mount root file system, and later times
> > out and crashes. I do see messages like
> >
> >    [  687.170573] IPv6: ADDRCONF(NETDEV_UP): vif3.0: link becomes ready
> >
> > from Dom0. But, presumably, requests from guest aren't reaching the NFS
> > server.
> >
> > Could you suggest if and what's wrong with my setup? Is NAT the right
> > mechanism for this purpose?
> >
> > Thanks.
> >
> > --
> > Jeenu
> >
> > [1] 
> > http://wiki.xen.org/wiki/Host_Configuration/Networking#Network_Address_Translation_.28NAT.29
> >
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Adam Goryachev Website Managers www.websitemanagers.com.au

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