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Re: [Xen-users] read only disk option in domUs

Steve Dobbelstein wrote:
list user <xktnniuymlla@xxxxxxxxxxxxxx> wrote on 04/25/2006 03:18:45 PM:

Hi all,

Successfully running a built from source xen 3.0.2-2 & linux 2.6.16 on
fedora 4 with lvm.

I'm trying to share a read only /usr across multiple domU's.

Logical volume "/dev/vg0/usr" is read only.  Within the domU's fstab
/usr is "ro".  Here is the disk option from the domU definition.

disk = [ 'phy:vg0/fc4,hda1,w' ,
         'phy:vg0/usr,hda2,r' ,
         'phy:vg0/swap,hda3,w' ]

This fails with an unable to write block error.

Now if the vg0/usr volume is specified with 'w' it works without
complaint until I try to use it in a different domU.  Then the complaint
is that it is already in use in another guest domain.

Q 1: is inability to specify a phy: as read only a bug?
Q 2: what is the proper way to share/use a read only volume among domU's?

Thanks for any help,
Mike Wright

We use a shared read-only device for /usr in our test setups quite
successfully.  The disk line in the domU config file looks like:
disk =
First device is /, second device is /usr, third device is shows up as a raw
disk for testing.  We are running FC4 in the domUs.

What is it that fails?  xm create? the boot up in the domU?

Thanks for your help.

It seems to be failing at an "fsck".  Here's a section of the boot:

Checking all file systems.
[/sbin/fsck.ext3 (1) -- /] fsck.ext3 -a /dev/hda1
/dev/hda1: clean, 177498/2048256 files, 1535857/2048000 blocks
[/sbin/fsck.ext3 (1) -- /usr] fsck.ext3 -a /dev/hda2
Error writing block 731 (Attempt to write block from filesystem resulted in short write).

        (i.e., without -a or -p options)
Last 2 lines repeat indefinitely.

In our setup I have seen an error or two during bootup in the domU because
something in the initialization wants to write to /usr.  It's usually some
function we don't care about so we ignore it.  Is something in your init
scripts trying to write to /usr?

Steve D.

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