RAID0 and Fedora 16 / f16

Sam Varshavchik mrsam at
Sat Nov 19 00:30:48 UTC 2011

Mark W. Jeanmougin writes:

> # fdisk -l /dev/sda
> Disk /dev/sda: 2000.4 GB, 2000398934016 bytes
> 255 heads, 63 sectors/track, 243201 cylinders, total 3907029168 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: 0x9e218bdf
>    Device Boot      Start         End      Blocks   Id  System
> /dev/sda1   *          63      530144      265041   fd  Linux raid autodetect

You need to move up the start of partition up to 2048, from 63. Grub won't  
fit here, as you've discovered.

> After the reboot I get:
> GRUB  loading.
> Welcome to GRUB!
> error: no such device: 71ec265a-f934-40a6-b02d-3ff3a274d229.

You need to:

1) Move partition 1 to start on logical sector 2048.

2) Use the workaround given there.

Both 1 and 2 are required to fix this. Neither one, by itself, will give you  
something that boots.

If you're doing a fresh install, this shouldn't be too bad. If you're trying  
to salvage a botched upgrade, you have to move up your sd[ab]1, before you  
can do anything. It can be done in rescue mode, but won't be easy. Given the  
size of the /boot partition, the easiest thing to do would probably be to  
temporarily copy /boto to one of your bigger partitions, resize it, and  
restore it.

Sounds easier than it actually is. fdisk won't be able to write out an  
updated partition table if something still has the disk mounted. So, you'll  
have to back up /boot, stop all disk arrays, use fdisk to gingerly remove  
partition 1 from both disks, and add it back it, slightly smaller, assemble  
a new mdraid array, being sure to specify version 1.0 raid superblock. mdadm  
will likely whine that it's still seeing its old superblock, with the wrong  
partition size. Just follow mdadm's instructions to zero it out. Reformat  
the slightly smaller sd[ab]1 as ext[34], start up all the arrays, mount  
everything back up, and restore your former /boot (and update the fstab on  
your root partition, to reflect the new /boot uuid).

Then you should be able to go into chroot /mnt/sysimage, and fix grub as  
instructed on the known issues page. Been there myself, have the wounds to  
prove it…

> If I do a "default" partitioning installation, then everything works
> fine, but I don't get RAID1. Or, any RAID at all. Just an LV spanning
> my drives.

… and you should get rid of LVM as well. It offers very few benefits for a  
generic RAID1 setup, like you have. Just use native primary/extended  
partitions, and mount them directly.

P.S. Your 256mb for /boot is a bit small-ish, these days, too.

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