Boot existing ubuntu server 12.04.5 from external hdd fails

[itbubbla]

Tried setting root set root='(hd1,msdos1)' but no luck. Still mounts in ro.

I also run fsck on the disk from my laptop, first run:

fsck from util-linux 2.27.1
e2fsck 1.42.13 (17-May-2015)
/dev/sdb1 contains a file system with errors, check forced.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/sdb1: 229973/9641984 files (0.2% non-contiguous), 2506316/38565632 blocks

Second run:

fsck from util-linux 2.27.1
e2fsck 1.42.13 (17-May-2015)
/dev/sdb1: clean, 229973/9641984 files, 2506316/38565632 blocks

Maybe I have to unplug the internal disk for this to work? I don't want to do that. It would have been easier if I somehow could tell the system to skip looking for the internal disk.
Or if there is any other way of backing up my postgres data without running postgres!? The files are on the disk but just copy them which I previously tried didn't work or maybe I did that wrong.

[darkod]

It's worth googling it a little. I know in ms sql you can attach db files to another server. Haven't tried anything similar in mysql or postgresql. Never needed to...
But some procedure has to exist. Look it up.