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

[list user <xktnniuymlla@xxxxxxxxxxxxxx>]

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 =
> ['phy:/dev/virt-blkdev-backend/dom1,sda1,w','phy:/dev/virt-blkdev-backend/usr,sda2,r','phy:/dev/virt-blkdev-disk_io_test/dom1,sda3,w']
> 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).
/dev/hda2: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY.
        (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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