Moving a server over to a RAID

[Tom H]

On Thu, Aug 19, 2010 at 2:13 PM, Mike A. Leonetti
<mikealeonetti at gmail.com> wrote:
>  (2010年08月19日 14:04), Tom H wrote:
>> On Thu, Aug 19, 2010 at 11:27 AM, Mike A. Leonetti
>> <mikealeonetti at gmail.com> wrote:
>>>  I have a server now that has one drive and is not set up on a RAID
>>> using Ubuntu 8.04.
>>>
>>> What I was going to do was boot with a Linux recovery disc, create a
>>> RAID1 manually with mdadm on two new drives, and then copy all of the
>>> data onto that then redo the boot partition.
>>>
>>> My question is, when I reboot, will Ubuntu automatically detect the RAID
>>> for me or are there modules I have to install ahead of time to make sure
>>> the RAID gets detected? Also, would anybody else handle the situation
>>> differently.
>> How many disks can your computer handle simultaneously?
>>
>> If three, then boot from your current install with all three, do a
>> full backup, install mdam, create the raid array on the two new disks,
>> boot from a Live CD, copy your data to the array (you will have to
>> install mdadm in the Live CD environment and activate the arrray),
>> modify the fstab, update the initrd, and install grub.
>>
>> If two. follow the same as above but create an array either with one
>> disk or with two disks with one missing. Once you replace the old disk
>> with the second new one, either grow the array or sync it.
>>
> It should be able to handle up to 4, which is fine. But according to
> Rashkae this setup won't work because of the following (to quote him):
>> When raid array's are created, they are given a "hostname", which, by
>> default, will by the system hostname.  By default, mdadm will not
>> auto-assemble raid arrays from a different hostname (to prevent
>> misunderstandings when hard drives are moved between different systems.)
> He also responded to this thread. I thought the same way you did until I
> read his comments.

First, if you crete the array while booted into your install, the
superblock will have the correct hostname. Otherwise it will not
auto-assemble but you will be able to assemble it manually and update
the superblock with the new host info.