[CentOS] Convert "bare partition" to RAID1 / mdadm?

Fri Jul 25 17:48:31 UTC 2014
Les Mikesell <lesmikesell at gmail.com>

On Fri, Jul 25, 2014 at 12:32 PM, Benjamin Smith
<lists at benjamindsmith.com> wrote:
> On 07/25/2014 06:56 AM, Robert Nichols wrote:
>> Unless you can figure out some way to move the start of the partition back
>> to make room for the RAID superblock ahead of the existing filesystem, the
>> answer is, "No." The version 1.2 superblock is located 4KB from the start
>> of the device (partition) and is typically 1024 bytes long.
>>
>>       https://raid.wiki.kernel.org/index.php/RAID_superblock_formats
>
> Sadly, this is probably the authoritative answer I was hoping not to
> get. It would seem technically quite feasible to reshuffle the partition
> a bit to make this happen with a special tool (perhaps offline for a bit
> - you'd only have to manage something less than a single MB of data) but
> I'm guessing nobody has "felt the itch" to make such a tool.
>
>
> On 07/25/2014 08:10 AM, Les Mikesell wrote:
>> What happens if you mount the partition of a raid1 member directly
>> instead of the md device?   I've only done that read-only, but it does
>> seen to work.
>>
>
> As I originally stated, I've done this successfully many times with a
> command like:
>
> mount -t ext{2,3,4} /dev/sdXY /media/temp -o rw

But if you write to it, can you clobber the raid superblock?  That is,
is it somehow allocated as used space in the filesystem or is there a
difference it the space available on the md and direct partition, or
something else?

-- 
   Les Mikesell
     lesmikesell at gmail.com