mdadm - is there a possible conflict?

[fmouse]

I'm updating some of the system software on a desktop box that's abysmally out of date, as Gentoo goes. The current mdadm on the box is v2.6.8. I want to update to v3.1.4. I have LVs and VGs built on top of my RAID arrays that have valuable data. If I emerge the newer mdadm, is it fully compatible with the config for v2.6.8? Is there anything I need to do, such as edits to /etc/mdadm.conf before doing this upgrade?

I really don't want to screw up here since mdadm v2.6.8 is no longer in the portage tree and if I do the update and there's a problem, I have no back-out path.

[DawgG]

i'd go about it very carefully - no matter what you decide to do, do at least one complete backup first and test it very thoroughly. don't try anything before that.

it's also not bad to have a 1:1 system-image (do it with rsync eg) that you can roll back - just in case.
do you want to update just mdadm or @system? because in the second case this will pull a lot of deps.
in the first case you just update mdadm and all of its deps, you still have the old binpkgs in case you need to roll back; also, the ebuild of the installed pkgs are in /var/db/pkg/CATEGORY/NAME/; you could use them in a portage overlay.

i think the cleanest way is to do a full backup and - if that works - do a complete system update. i've had problems with the devices created by mdadm 3.1.4: they always had devicenames like /dev/md127 until i recreated them with