External array showing as /dev/sda

David Hubbard dhubbard at dino.hostasaurus.com
Sun Mar 21 15:59:29 CDT 2010

From: Behalf Of J. Epperson
> I'm somehow missing how getting the non-installable smaller 
> GPT VD to be /dev/sda will change that scenario. The other
> responder echoed one of my initial thoughts when he suggested
> turning off the external array.  That should do it.

If I could get the internal raid controller to be
/dev/sda, then the RHEL/centos installer will not
care about the fact that the external array is
too big and would require GPT to boot off of, then
the installer would let me proceed.   It was only
an issue with it being /dev/sda since that made the
installer think there was no way to writen an MBR
and boot off of it.

But, unplugging external did lead me the right direcation.
What I've had to do is this:

1) Internal array I had desired to be single RAID 50
across 8 drives.  Thanks to Dell's choice of LSI
for their current raid controllers and LSI missing
the feature that most others seem to have in being
able to present parts of one array as multiple
logical drives, I ended up having to waste the first
two drives to make a RAID 1 mirror smaller than 2 TB
and then only six remaining drives in the RAID 50.

2) Unplugged the external array and installed centos
using normal non-GPT boot to the raid 1 virtual
drive.  It installed to /dev/sda.

3) After install, edit /boot/grub/device.map and
changed it to show:

(hd0) /dev/sdb


grub> device (hd0) /dev/sda
device (hd0) /dev/sda
grub> root (hd0,0)
root (hd0,0)
 Filesystem type is ext2fs, partition type 0x83
grub> setup (hd0)
setup (hd0)
 Checking if "/boot/grub/stage1" exists... no
 Checking if "/grub/stage1" exists... yes
 Checking if "/grub/stage2" exists... yes
 Checking if "/grub/e2fs_stage1_5" exists... yes
 Running "embed /grub/e2fs_stage1_5 (hd0)"...  15 sectors are embedded.
 Running "install /grub/stage1 (hd0) (hd0)1+15 p (hd0,0)/grub/stage2
/grub/grub.conf"... succeeded

4) Reboot, connect external array while server is
rebooting, comes back up and boots off of internal
array from bios, grub is happy because now it is
set up for /dev/sdb.

Only downside to this situation is if something were
to fail and take the external array down the server
won't boot since internal will go back to being
/dev/sda.  But if the external array is down then
we've got issues anyway. :-)



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