External array showing as /dev/sda

Frank Wang wg at yarbs.cn
Mon Mar 22 01:59:13 CDT 2010

Hi David,
    We used to have similar problem in our R710 when the 6x750G RAID5
array exceeded the 2T boundary. We used an usbstick(2G) as the /boot
partition and put grub on that to boot the Centos. Then anaconda won't
complain the huge GPT partition anymore.
    The usbstick can be plugged into the internal usb socket in the
chassis, saving the trouble mishandled accidentally. Even the
stability of an usbstick is usually not as good as a hard disk, you
can always save a backup one, it's so cheap nowadays after all.

Frank Wang

On Mon, March 22, 2010 4:59 am, David Hubbard wrote:
> 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
> Then:
> grub
> 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.
> succeeded
>  Running "install /grub/stage1 (hd0) (hd0)1+15 p (hd0,0)/grub/stage2
> /grub/grub.conf"... succeeded
> Done.
> 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. :-)
> Thanks,
> David
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