[CentOS] CentOS 5 grub boot problem

Wed Aug 5 20:54:08 UTC 2015
Bowie Bailey <Bowie_Bailey at BUC.com>

On 8/5/2015 4:00 PM, Chris Murphy wrote:
> - Ahh OK now I see why I was confused. The originally posted partition
> map uses cylinders as units, not LBA. I missed that. Cylinder 1 is the
> same as LBA 63. And that is sufficiently large for a GRUB legacy stage
> 2.
> - OK this is screwy. Partitions 1 and 3 on both drives have the same
> number of sectors, but partitions 2 differ:
> /dev/hde2             401,625   975,691,709   975,290,085  fd Linux
> raid autodetect
> /dev/hdg2             401,625 1,952,491,904 1,952,090,280  fd Linux
> raid autodetect
> That can't work as these are two partitions meant to form /dev/md2 and
> need to be the same size.

That's because I'm intending to increase the size of that filesystem.  
The raid should work as long as the new partition is at least as big as 
the old one.  Once I get this working, I will remove the original drive 
and add another 1TB drive so both partitions are the same (larger size) 
and extend the filesystem into the new space.

> - Also, 401625 is not 8 sector aligned. So it's a double whammy and
> since it has to be repartitioned anyway you might as well fix the
> alignment also.
> First off fail+remove hdg2 (you need to confirm I've got the devices
> and commands right here):
> mdadm --manage /dev/md2 -f /dev/hdg2 -r /dev/hdg2
> mdadm --zero-superblock /dev/hdg2
> Using fdisk delete hdg2, then make a new primary partition (partition
> 2) and hopefully figure out how to get it to do LBA rather than CHS
> entry; or use parted which can but it's UI is totally unlike fdisk.
> The start sector for hdg2 should be 401623 which is 8 sector aligned,
> and the end value should be 975691717 in order to make it the same as
> hde2. And change the type to 0xfd.
> Now you probably have to reboot because the partition map has changed,
> I'm not sure if partprobe exists on CentOS5, could be worth a shot
> though and see if the kernel gets the new partition map. Check with
> blkid.
> And then finally add the "new" device.
> mdadm --managed /dev/md2 -a /dev/hdg2
> And now it should be resyncing...
> cat /proc/mdstat

But if both hde and hdg are using 401625, then wouldn't I have to 
repartition both drives so the sizes match?

I'm still not sure that this is a partitioning problem.  I did not have 
any problems create the partitions or syncing the three raid devices.