# Resize RAID1 array without knowing which disk is which


I want to grow my RAID1 array from 2x250GB to 2x500GB. The
[following resource](http://www.steveglendinning.com/2007/10/24/)
has helped my a lot. 

> Update
>
> It all worked, allthough the kernel decided to crash during the
> offline ext4 resize. But I finally have my extra disk space
>
> `% df -h | grep md6`
>
> before: `/dev/md6               77G   67G  6.7G  91% /vol`
>
> after:  `/dev/md6              306G   67G  224G  23% /vol`

Now to my problem/solution:

On Linux you often have the following problem: You are 
*looking* or *touching* some piece of hardware and 
you are asking yourself: "is this card `eth0` or `eth1`?"
or "is this disk `/dev/sda` or `/dev/sdb`?".

In my case I didn't know which disk had what device name. Solution?

Rip out a random disk and replace it with an empty new disk (no
partition) and hope for the best.

> Some scary moments come to pass

Well after rebooting, I got the question if I wanted to boot the
degraded array. After saying 'yes' I was back into my system.

Turns out I had ripped out `/dev/sda`. Time to mark this on the
case:

<img src="/images/2009/case-markings.jpg" alt="Case Markings" />

Now to restore the partition table of the old disk to the new one:

    sfdisk /dev/sda < sda.sfdisk

Where `sda.sfdisk` is the partition info saved with `sfdisk -d
/dev/sda`.

Now my last partition on the disk was `/dev/sda4` - luckily *not* in a logical
partition, as I don't know how to extend that. So I could easily delete this
partition and recreate it so that it fills the entire size of the new
disk. Some simple `fdisk`-foo will help you here.

Now re-add all the partitions back to the RAID1 array:

    mdadm --add /dev/md0 /dev/sda1

And this for all 8 partitions.

And then... we wait for the RAID1 rebuild:

    watch cat /proc/mdstat

<img src="images/2009/compu-at-work.jpg" alt="Computer at work" />

Just to be sure I re-installed `grub` with `grub-install /dev/sda`.

Rinse and repeat for the other disk and after that has finished
rebuilding I can resize the file system on `/dev/sda4`. Which is

    % grep sda4 /proc/mdstat 
    md6 : active raid1 sda4[2] sdb4[1]

So

    e2fsck -f /dev/md6
    resize2fs /dev/md6

Note this was all done with kernel 2.6.29.1 and the `ext4` file system.
See 
[this post](/2009/march/29/ubuntu_9_04__2_6_29__ext4_and_server_move/index.html) 
or some info on that. And only 1 kernel crash during the offline resize!