[Xen-users] Inaccessible Disk

[Stephen Nelson-Smith <sanelson@xxxxxxxxx>]

Hello,

I'm a fairly experienced Xen user, with a large number of guests in
production running atop CentOS 5.

The time has come to refresh this infrastructure, and I've selected
Fedora as the Dom0 platform.  For now I'm just running some tests on a
test box, but I'm running into some unexpected problems.

I'm using Fedora 17, which gives me:

[root@dom0-a xendomu]# xm dmesg | grep "Xen version"
(XEN) Xen version 4.1.4 (mockbuild@[unknown]) (gcc version 4.7.2
20120921 (Red Hat 4.7.2-2) (GCC) ) Tue Dec 18 22:30:42 UTC 2012

I've tended to use virt-install as my standard tool, in the past, so I
had a go with this initially.

I've created a logical volume:

[root@dom0-a xendomu]# pvs
  PV         VG      Fmt  Attr PSize   PFree
  /dev/sdb   xendomu lvm2 a--  298.09g 294.09g
[root@dom0-a xendomu]# vgs
  VG      #PV #LV #SN Attr   VSize   VFree
  xendomu   1   1   0 wz--n- 298.09g 294.09g
[root@dom0-a xendomu]# lvs
  LV   VG      Attr     LSize Pool Origin Data%  Move Log Copy%  Convert
  g1   xendomu -wi-a--- 4.00g

And then ran:

virt-install --name g1 --ram 500 --disk path=/dev/xendomu/g1
--location http://mirror.centos.org/centos/6/os/i386

As expected this gave me a text installer, which I went through in the
usual fashion.  The install ran all the way through, but on reboot I
received  the message:

error: POST operation failed: xend_post: error from xen daemon:
(xend.err "Disk isn't accessible")

root@dom0-a xendomu]# virsh start g1
error: Failed to start domain g1
error: POST operation failed: xend_post: error from xen daemon:
(xend.err "Disk isn't accessible")

Here's the config:

[root@dom0-a xendomu]# virsh dumpxml g1
<domain type='xen'>
  <name>g1</name>
  <uuid>65d06e7c-a69e-3f4a-d403-b5168fb56d5f</uuid>
  <memory unit='KiB'>512000</memory>
  <currentMemory unit='KiB'>512000</currentMemory>
  <vcpu>1</vcpu>
  <bootloader>/usr/bin/pygrub</bootloader>
  <os>
    <type>linux</type>
  </os>
  <clock offset='utc' adjustment='reset'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <disk type='block' device='disk'>
      <driver name='phy'/>
      <source dev='/dev/xendomu/g1'/>
      <target dev='xvda' bus='xen'/>
    </disk>
    <interface type='bridge'>
      <mac address='00:16:3e:af:bb:f6'/>
      <source bridge='virbr0'/>
      <script path='vif-bridge'/>
    </interface>
    <console type='pty'>
      <target type='xen' port='0'/>
    </console>
  </devices>
</domain>

The device surely exists:

[root@dom0-a xendomu]# ls -l /dev/xendomu/g1
lrwxrwxrwx. 1 root root 7 Dec 31 20:46 /dev/xendomu/g1 -> ../dm-0

[root@dom0-a xendomu]# fdisk -l /dev/xendomu/g1

Disk /dev/xendomu/g1: 4294 MB, 4294967296 bytes
255 heads, 63 sectors/track, 522 cylinders, total 8388608 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00082140

           Device Boot      Start         End      Blocks   Id  System
/dev/xendomu/g1p1   *        2048     1026047      512000   83  Linux
/dev/xendomu/g1p2         1026048     8388607     3681280   8e  Linux LVM

Puzzled as to why this doesn't work, I decided I'd try a different approach:

dd if=/dev/zero of=/srv/xendomu/centos6.img oflag=direct bs=1M seek=3800 count=1
wget http://mirror.centos.org/centos/6/os/i386/isolinux/vmlinuz -O
/boot/vmlinuz-xen6-install
wget http://mirror.centos.org/centos/6/os/i386/isolinux/initrd.img -O
/boot/initrd-xen6-install
cat <<EOF > /etc/xen/centos6
kernel = "/boot/vmlinuz-xen6-install"
ramdisk = "/boot/initrd-xen6-install"
name = "centos"
memory = "512"
disk = [ 'tap:aio:/srv/xendomu/centos6.img,xvda,w', ]
vif = [ 'bridge=virbr0', ]
bootloader="/usr/bin/pygrub"
vcpus=1
on_reboot = 'destroy'
on_crash = 'destroy'
EOF
[root@dom0-a xendomu]# xm create -c centos6
Using config file "/etc/xen/centos6".
Error: Disk isn't accessible

I'm getting the impression I'm missing something fundamental here....

Any hints / suggestions?

Thanks,

S.

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