First of all: I know I do not post a new ROM here, and also I know that this isn't the usual way to clear things, I hope the mods can forgive me, I will explain why I start this thread.
First of all, the problem: As a lot of you noticed, when you try an ICS-based ROM like CM9 or any of those MIUI v4-clones, your external SD-card is gone. Normally you find all your data at /sdcard/external_sd/, and now you go to that folder with a file explorer to see that it's empty.
A lot of those guys now post in the threads of these ROMs complaining about lost data and stuff, sometimes getting an answer, sometimes not. The workaround is the same on all these ROMs, but most of the ROM devs do not add this fix to their start-postings.
As no one reads a full 300+-pages thread, the solution for this problem gets lost ("Didn't you read the solution on page 153?" ). This is why I start a new thread to link on, with a full tutorial, even pictures are added, yaaay.
Again: This is no new solution, I didn't code anything new.
So this is how you do it:
First of all go to this thread and download the apk for Directory Bind. Install it.
This app was built to move data to your external SD to get more space on your internal memory, we use this app in a different way.
When you use a file explorer with root permissions, you will see that your external SD can be found at /mnt/emmc/. This folder is unhandy to use, as most applications aren't built to access any directories outside /sdcard/ (would need root permissions). [I once saw a ROM where the external SD was mounted to /mnt/ext_sdcard/, if that's the case in your ROM, just do it the same way ]
So you start Directory Bind, tap on the menu button and add a new entry. Use these settings:
As you see, all data that's in /emmc/ (do NOT forget the slash at the end!) should get mounted to /sdcard/external_sd/ (again: don't forget the slash). Do NOT tick the "Transfer files from target to data"-Button, as this would cause the whole external SD to be copied onto your internal memory!
After tapping "Add", you should see a new entry in your list of bindings. Tap on the disc-icon in front of that entry, so it becomes green:
If the icon becomes red, check if you have any spelling mistakes in the paths you used or if /emmc/ is the correct path for your SD-card [see /ext_sdcard/-issue above].
If all went well, tap the menu-button again and open the preferences. First of all enable the box at the top, saying "Bind on boot". I hope I don't have to explain why
Second, scroll down to the bottom and enable the "Alternate dbase mgmt"-Box. This isn't 100% neccessary, it can work without this option. I tested two devices and both had to have this option enabled to keep the settings after a reboot. To be sure, just enable it.
You can now close Directory Bind and check your /sdcard/external_sd/-folder again to see everything is there! Reboot to check if you were successful in the whole "bind on boot"-thing.
That's it, gl&hf with it