On Tue, Jan 20, 2004 at 11:58:41PM -0500, Hubert Chan wrote: > >>>>> "Johannes" == Johannes Graumann <[EMAIL PROTECTED]> writes: > > [...] > > Johannes> And on another note: in > Johannes> > http://www.mirrors.wiretapped.net/security/cryptography/filesystems/loop-aes/loop-AES.README > Johannes> I read the following: "Don't use a journaling file system on > Johannes> top of file backed loop device, unless underlying file system > Johannes> is journaled and guarantees data=ordered or data=journal." > Johannes> Can anybody comment on whether I can use reiserfs on top of my > Johannes> loopback? > > The comment has nothing to do with whether or not your encrypted > filesystem is a journaling filesystem with or without data=ordered.
Actually, it does. > It > has to do with using a file-backed loop device (versus partition-backed > loop device), where the file is sitting on a journaling filesystem. If > your loop device is a partition, or is file-based, but sits on top of a > non-journaled filesystem Wait a second; I think this one doesn't belong in the list of things that will be correct. > or a journaled filesystem with data=ordered or > journaled, then you can use any filesystem without problems. (Or, at > least, you won't (shouldn't) run into any problems other than what you > might run into if it were not on a loopback device.) > > Basically, if you don't have data=ordered, or data=journaled, any system > crash could completely screw up your entire loopback, rendering it > completely unusable. If you don't plan on having any system crashes or > hard reboots, I think you can still run a loopback on top a > non-data=ordered journaled filesystem fairly safely. No, the point is that journaling file systems depend on stuff being written to disk in the order they want, so if something goes wrong at _any_ moment, they can pick up the pieces. ext3 with data=writeback, for example, only bothers to strictly control the order of metadata. A loopback to a file on such a filesystem will not preserve write ordering, so a journaling filesystem on top of it will be making false assumptions. Filesystem metadata (which needs to be ordered) is just data on the loopback device. However, if the underlying filesystem preserves data ordering, it can satisfy the requirements of the journaling filesystem that's on top of it. I'm not sure if you need data=journal on the underlying filesystem for data=journal on the loopback filesystem to make sense, but I don't think so. -- #define X(x,y) x##y Peter Cordes ; e-mail: X([EMAIL PROTECTED] , des.ca) "The gods confound the man who first found out how to distinguish the hours! Confound him, too, who in this place set up a sundial, to cut and hack my day so wretchedly into small pieces!" -- Plautus, 200 BC
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