Because logical volumes (LVs) can be resized at runtime i need a
filesystem (FS) feature which enables ext2 to be extended/reduced
while its mounted too. This could be an extension to tunefs or a
separate FS administration tool.
You know what you ask.....
Resizing an ext2 filesystem is difficult. Reducing is obviously much
harder, but even in the extending cases, in some cases you will need to
move disk blocks around to make space for the larger block group
descriptors.
The hardest thing to deal with, and it's an issue even with Miguel's
patches, is what to do when you want to remove a physical disk located
in the middle of an ext2 filesystem. Not only do you have to worry
about moving data blocks off, but over the long term, there are (disk)
address fragmentation issues that come up as well.
It's possible, although nontrivial, to do this off-line. Doing this
while the filesystem is mounted, and possibly active, is much, much
harder.
- Ted