http://loop-aes.sourceforge.net/loop-AES.README2.2. Use of journaling file systems on loop device
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Don't use a journaling file system on top of file backed loop device. Device
backed loop device can be used with journaling file systems as device backed
loops guarantee that writes reach disk platters in order required by
journaling file system (write caching must be disabled on the disk drive, of
course). With file backed loop devices, correct write ordering may extend
only to page cache (which resides in RAM) of underlying file system. VM can
write such pages to disk in any order it wishes, and thus break write order
expectation of journaling file system.
This comment even claims it is dangerous to do so:
http://mail.nl.linux.org/linux-crypto/2 ... 00027.htmlAbsolutely - journaling filesystems depend upon the maintenance of
the order of device write operations. Where this is not the case, file
system recovery based upon the journal has the potential to be very
dangerous.
Thus journaling in a file-backed loop device (such as Puppy uses) has the potential to cause the very problem journaling was supposed to prevent!
This has nothing to do with encryption per se. It does turn up in encryption discussions though, because that is where file-based loop devices are often used.
I mentioned this on the other forum but it drew no comments. Is this something that should be re-thought? Should we be using ext2? Or am I completely missing some point here? I'm wondering if the operative phrase is "on top of", that is, the file system underlying the loop device can be journaling, but creating another loop device within, that is journaling, is the problem?