root@feld-bert:/home/markus# LANG=C e2fsck -n -C0 /dev/dm-1
e2fsck 1.42-WIP (16-Oct-2011)
e2fsck: Group descriptors look bad... trying backup blocks...
Error writing block 1 (Attempt to write block to filesystem resulted in short write). Ignore error? no
[more errors of this kind]
e2fsck: Device or resource busy while trying to open /dev/dm-1
Filesystem mounted or opened exclusively by another program?
1. e2fsck should not try to write when using -n.
2. ignore error is not a question to be answered with "no" when using -n but with "yes" instead.
3. I do not know what that "Device or resource busy" error is about (someone else reported that problem on email@example.com, I'm merely relaying that bug report), but it doesn't matter either: -n means don't write and reading worked obviously.
Full log @ http://pastebin.com/raw.php?i=x0siBmrj