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
Recently, it seems that RHEL/CentOS is smart enough to automagically create /dev/mdX when inserting a drive "hot" EG: USB or hot swap SATA, so I haven't had to do this for a while. You can, however do this, which seems to be logically equivalent:
mdadm --manage /dev/mdX --stop; mount -t ext{2,3,4} /dev/sdXY /media/temp -o rw;
-Ben