create raid1 on a installed system

[Asif Iqbal]

On Sun, Jul 19, 2009 at 9:55 PM, Rashkae<ubuntu at tigershaunt.com> wrote:
> Brian McKee wrote:
>> On Sun, Jul 19, 2009 at 6:29 PM, Asif Iqbal<vadud3 at gmail.com> wrote:
>>> I have two disks on my x2100, sda and sdb, both are 80GB. I installed
>>> jaunty server on sdb1.
>>>
>>> How do I now create software raid1 short of reinstalling the OS on
>>> software raid disk md0  ?
>>
>> Create the raid on sda1 with the other disk 'missing'
>> Copy sdb1 to md0, remove sdb altogether and reboot to md0, and test to
>> make sure you got it right, then reformat sdb and add it to the
>> degraded array.
>>
>> This might be helpful
>> http://www.debian-administration.org/articles/238
>>
>> Brian
>>
>
> There is one huge gotcha with this process.
>
> When you boot to md0 for the first time, the system will fail to detect
> the raid array and after a long wait, dump you to busybox shell.
>
> This is because when you built the raid array from a working system, the
> array gets tagged with your system hostname.  When the system is booting
> from initrd, mdadm (the program that is responsible for detecting and
> assembling the array) by default will only assemble arrays that match
> the current hostname (which in initrd environment is blank).
>
> Be sure you have a print-out copy of the mdadm man page.  You should be
> able to give it the appropriate incantation from busy-box that will
> update the hostname in the array and all will thereafter be well.

I also noticed that article is pretty old (from 2005) and using
mkinitrd instead of mkinitramfs.

Would be nice if there is an updated howto relevant to new features really.

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-- 
Asif Iqbal
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