seperating current profile builds from old ones

[Stefan Huchler <stefan.huchler@mail.de>]

I was so cracy that I installed nixos on a 16gb chromebook. which makes
every update now very hard, because of space problems.

So well then I thought I have this 64gb sd(hx?) card lets just move the
whole /nix/store there. But when I run a hdparm -tT performance test I
got I think 17mb/s vs 170mb/s read results sdcard vs internal flash.

So I would prefer to not slow my complete system down by putting it
completly on the sdcard, but I would like to have some history to revert
back to something.

Is there a way to keep only the packages form the current profile on the
internal flash and move old stuff to the sdcard?

Or should I use some sort of raid (btrfs maybe) to spread the files over
both devises.

I also thought about putting all on the sdcard but have a very big swap
file on the internal flash. But I think the System dont has to swap much
on my setup. so the first read would be where it counts.

Or maybe just install for the user the packages he needs most under his
user profile, like the browser which I restart very often.

Is there some nixos-way to do that?

Or any suggestions would be nice.

Thanks