Moving from Debian Wheezy - 32bit to 64bit

[Sam Martin <sambomartin@gmail.com>]

I've made a bit of an error with a new NAS / HTPC i've setup.

Only after a few weeks, I've realised I've put the 32bit version on rather than the 64bit dist. 

Aside from the inconvenience of having to fluke my way through user config, samba, ftp, xbmc, etc. more worrying for me is a raid volume i've set up using mdadm.

I'm really new to linux and software raid, and not entirely confident the linux installer wont touch the raid volume.

I've been on IRC #debian and the guys there recommended booting to linux from usb and copying os as it to it as a backup.

I'm thinking the steps would be something like:

dismount raid vol
shutdown
physically disconnect hdds in raid vol
boot to linux from usb
copy sdd (where os is) to usb
format ssd
install 64bit dist
start up
make sure it's ok?
shutdown
reconnect hdds there were in raid
startup....

how do you get mdadm to load the raid vol again?

I couldn't find anything in the /etc/mdadm config

Also, will i need to do anything with file permission before i do this?
Not sure how mdadm raid works, but is there a way I can "import" raid vol without having to rebuild it?

I absolutely don't want to lose anything, so really welcome any advice you can give me.

Many thanks,
Sam