To avoid messing around on the internal flash partition, it's a good idea to work on a network drive when playing around. NFS is the de-facto protocol for this.
I experienced some problems with the default NFS options (timeouts, lockups, etc), and some experimentation shows this works quite ok:
mkdir /tmp/root mount -t nfs <server ip>:/tmp/revica/root /tmp/root -o rsize=1024,wsize=1024,soft,nolock
Your mileage might vary.
You can backup your reciva root to nfs with a spell like:
tar -cvf /tmp/root/root.tar /bin /boot /dev /etc /lib /linuxrc /opt /root /sbin /usr /var
we don't use wildcards for tar, because we don't want to recurse across mount points and start tarring up nfs, and busybox tar can't avoid that - so we have to specify all the root folders we want to backup.
My NFS server is an NSLU2 micro-NAS running debian.