Internal SD-card hardware erros. Is there a way to move partitions to external sdcard?
On Android it's not that easy to modify the "fstab", as that's often stored inside the boot-image (see Wikipedia on "initrd" for a more detailed explanation).

However, depending on the device, there might be alternative solutions. Some of them would be:


DirectoryBind binds "directories located on external_sd to directories on internal memory (/sdcard). This way You can transfer large application data directories to external_sd." (in other words, you could compare that with "symbolic links", pointing to the external SDCard). See also this article.
Swap Internal and External sdcard. According to the linked article, this should work for ANY Android Phone or Tablet. This solution is comparable to your "editing of fstab".
Root External 2 Internal SD is an app to swap the cards. From its description, it does the same as described in the previous point.


There might be more solutions around, but these are the ones I've heard of. Hope one of them can help you out!