On Wednesday, 18 August 2010 21:45:56 +0300,
Nikolai K. Bochev wrote:

> Strange, i did 2 clean installs of centos 5.5 on an ubuntu 9.10 host
> and it went flawless with virtio devices ( both disks and network ).

Doing some tests with CentOS 5.5 on a KVM virtual machine, after doing
the installation, I added a second disk. But when trying to boot from
it, I get the following error:

---------------------------------------------------------------------
root (hd1,0)

Error 21: Selected disk does not exist
---------------------------------------------------------------------


The two disks are Virtio devices that are recognized when booting from
the first disk:

---------------------------------------------------------------------
[root@localhost ~]# fdisk -l /dev/vda

Disco /dev/vda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Unidades = cilindros de 16065 * 512 = 8225280 bytes

Disposit. Inicio    Comienzo      Fin      Bloques  Id  Sistema
/dev/vda1   *           1        1174     9430123+  fd  Linux raid autodetect
/dev/vda2            1175        1305     1052257+  fd  Linux raid autodetect
[root@localhost ~]#
[root@localhost ~]#
[root@localhost ~]# fdisk -l /dev/vdb

Disco /dev/vdb: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Unidades = cilindros de 16065 * 512 = 8225280 bytes

Disposit. Inicio    Comienzo      Fin      Bloques  Id  Sistema
/dev/vdb1   *           1        1174     9430123+  fd  Linux raid autodetect
/dev/vdb2            1175        1305     1052257+  fd  Linux raid autodetect
---------------------------------------------------------------------

The idea of these tests is to set up software RAID1 on a running system,
since, it seems that Anaconda does not support installation on degraded
RAID.

But I'm not sure if this is a problem of Virtio or that GRUB is not
recognizing the second disk.

I made sure to modify /boot/grub/device.map with the entry for the new
disk:

---------------------------------------------------------------------
[root@localhost grub]# cat /boot/grub/device.map
# this device map was generated by anaconda
(hd0)     /dev/vda
(hd1)     /dev/vdb
---------------------------------------------------------------------

And the reconfiguration of GRUB on both disks did not give problems:

---------------------------------------------------------------------
[root@localhost grub]# grub --device-map=/boot/grub/device.map


    GNU GRUB  version 0.97  (640K lower / 3072K upper memory)

 [ Minimal BASH-like line editing is supported.  For the first word, TAB
   lists possible command completions.  Anywhere else TAB lists the
possible
   completions of a device/filename.]
grub> root (hd0,0)
root (hd0,0)
 Filesystem type is ext2fs, partition type 0xfd
grub> setup (hd0)
setup (hd0)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/e2fs_stage1_5" exists... yes
 Running "embed /boot/grub/e2fs_stage1_5 (hd0)"...  15 sectors are
embedded.
succeeded
 Running "install /boot/grub/stage1 (hd0) (hd0)1+15 p
(hd0,0)/boot/grub/stage2 /boot/grub/grub.conf"... succeeded
Done.
grub> root (hd1,0)
root (hd1,0)
 Filesystem type is ext2fs, partition type 0xfd
grub> setup (hd1)
setup (hd1)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/e2fs_stage1_5" exists... yes
 Running "embed /boot/grub/e2fs_stage1_5 (hd1)"...  15 sectors are
embedded.
succeeded
 Running "install /boot/grub/stage1 (hd1) (hd1)1+15 p
(hd1,0)/boot/grub/stage2 /boot/grub/grub.conf"... succeeded
Done.
grub> quit
quit
---------------------------------------------------------------------


Any idea what may be causing the problem?

Regards,
Daniel
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