It's simple, there are no real benefits to moving only part of the OS to an SD card rather than the whole thing.

It's possible, but it's an inferior solution. The problem is that the user wants more space to install applications. The good solution is to move the OS to a card where there is lots of space available. The bad solution is to start symlinking stuff to the card (I outlined the reasons above).

Because important parts of your OS are still residing on the slower built-in flash memory.

Why does having two hard drives running at the same time use more power than just one?

Why is RAID 0 less reliable? You've doubled your failure points and removed the option of a bootable backup.

No, I suggested that the solution of only moving portions of the OS to a flash card was less reliable than booting the whole OS from that flash card.

As I said above, you've doubled your failure points.

For the most part, yes.

Booting from a flash card gives you a number of benefits. It leaves a bootable backup on the internal flash that you can fall back to if something goes wrong, it speeds up filesystem-intensive operations (uncompressed filesystem, faster flash memory), and it offers you lots of space to install applications.

A question for you, Master of Gizmo, with all those benefits (and all the disadvantages of symlinking) why would you rather symlink stuff to your card than boot from it?

What's wrong with symlinking ?
Does it matter anything that the data actually resides on a (of course ext3 formatted) memory card or in the internal flash ?
I want to try it to symlink large libraries to a folder on the memory card, I didn't try it yet.

GA is right, symlinking is just a world of pain. Been there, done that. Too many things can go wrong, too many hidden gotcha's. Moving your boot to a card seems scary at first, but it is the correct long term solution. Not to mention you get a 'free' fallback boot in case something goes amiss on the 'main', card based boot.

No, ext3 is the wrong choice.

This is a flash memory device, so you should better use JFFS2.
it keeps up the live of your memory card.


About symlinking:

I'm now too at the point to get more space for the OS.
Symlinking looked like a good idea at the first place, but there is a problem.
From my experience connecting the N810 via USB to a PC can result in making the large internal flash memory (2GB) not usable on the N810 Device during the time, the device is connected to the PC.

So if you moved /usr to the flash drive and mounted it on /usr,
the device will brake because it can't use the flash memory as described above.

If you only copied /usr to the flash drive and mounted the flash drive on /usr, you mights still be able to use the device but without the apps installed on the large flash drive.
Additionally dpkg the packet manager will now run in problems if you now update or install new software because as i said, the large 2 GB flash drive is hidden, when connected to the PC, so the N810 device uses the small 256 MB one which is inconsistent to the apt database you used for the larger 2 GB flash drive.


So from this viewpoint installing a new independant system on the large internal flash drive is better than symlinking.