Xen users - Apr 2009 - can not start guest domain exported from NFS

Dear All:
I am using Xen 3.3 on a Fedora 8 machine and failed to start a guest
domain from an exported NFS directory.
The step I follow is as follows
NFS server: 192.168.1.1
NFS client:  192.168.1.201
1: I copy the guest.img, which can be corrected booted on NFS client
to the NFS server.
2: On the NFS server
    mount guest.img  /xen/guest; such that if I do a ls /xen/guest, I
can see all the files under /xen/guest
        Then I exported /xen/guest to the Client
3: On the NFS client side
     mkdir /xen/guest
     mount 192.168.1.1:/xen/guest  /xen/guest
     Do a ls /xen/guest on the NFS client, I can see the files correctly.
Then I changes the xen config file as follows.
kernel="/boot/vmlinuz"
ramdisk="/boot/initrd...."
root="/dev/root"
nfs_server="192.168.1.1"
nfs_root=/xen/guest

When I boot the guest domain, the error is it can not file the
/dev/root, ie., the root file system. Anyone can help me. Thanks.

- Steven

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On Fri, Apr 17, 2009 at 8:28 PM, Steven <wangwangkang@gmail.com>
wrote:
> Then I changes the xen config file as follows.
> kernel="/boot/vmlinuz"
> ramdisk="/boot/initrd...."
> root="/dev/root"
> nfs_server="192.168.1.1"
> nfs_root=/xen/guest
>
> When I boot the guest domain, the error is it can not file the
> /dev/root, ie., the root file system. Anyone can help me. Thanks.
Short answer, nfs root needs a special setup, more than just editing
xen config file.

In the old days (last time I use nfs root was many years ago) the
kernel needs to be able to configure IP address by itself without
tools like "ifconfig". Then it needs nfs client support built in, not
as a module. Those requirements may not be there anymore if you have a
specialized initrd, but again it requires special setup. I''m not sure
such functionality is enabled by default in "normal" kernels (like
Centos or xen.org kernel).

These link might give you some info
http://www.virtuatopia.com/index.php/CentOS_5_-_Build_a_Custom_Xen_Kernel_with_NFS_Root_Filesystem_%28CONFIG_ROOT_NFS%29_Support
http://www.itp.uzh.ch/~dpotter/howto/diskless

You didn''t say what your primary purpose for nfs root is. If
it''s only
to have centralized storage (to ease live migration, for example),
it''s MUCH easier to either :
- use iscsi on domU and setup domU to have iscsi root.
- use iscsi on dom0, setup domU normally on iscsi-imported block device
- store domU image on nfs

Regards,

Fajar

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