That is the same question I have. And I found some help on a similar (German) forum. I might translate what we ended up reasoning there...
Here it is, maybe let it run through a translation engine:http://forum.nas-portal.org/showthread.php?t=6610
We hypothesize that CPU and OS are pretty much the same on the 2big as on the edmini V2. Thus, we do have utelnetd and also dropbear (I compiled it natively on my hacked edmimi V2). Here is the link for edmini V2 dropbear:http://mitglied.lycos.de/jhench/dropbear/dropbear-0.52_armv5tejl.tar.gz
The question is just how to get that onto the 2big. I am currently in the process of decision whether to buy the 2big and to replace my edmini setup with this more secure option (RAID 1) versus rsync to an external USB.
My guess is that once we are able to modify the system partition from inside the system (i. e. after having access) these changes will be stored on the "update partition" of the drive. And this partition is highly likely to be RAID1, as well as the r/o base system partition.
Once we are running in RAID1, our own modifications will be stored like updates (as on the edmini V2), however on both drives simultaneously. What will be more troublesome is to get the backdoor (http shell, utelnetd and / or dropbear) on the RAID 1 in first place.
One way would be to mount both drives on another computer as RAID 1 and to then apply the change (to the future r/o partition or the update partition). Another way might
1. to run the 2big
2. to take out one drive while running, i.e. to simulate an HD failure
3. to shut it down in 1 drive state
4. to modify the drive that had remained in the 2big longer (make sure for correct time stamps), e.g. by connecting the drive to a linux machine to add our "backdoor"
5. to boot the 2big in 1 drive state with the modified drive
6. to now add the unmodified drive as if it was a replacement
7. to hope that the RAID 1 system will agree with our theory and will copy the changes to the new drive as it would with updates.
In theory it is enough if we can copy just one single file onto the system, i.e. the webserver shell backdoor (as described e.g. here: http://lacie.nas-central.org/wiki/SuccessStories
). That is enough to copy all other files directly on the running machine in RAID 1 mode to the respective places.