> List members:
> I am currently using the ext2fs under RH7.1 running kernel 2.4.2-2.
> I am considering the implementation of either the SGI XFS or ReiserFS
> journaling file system ("JFS"), I plan to try XFS first. One of the issues I
> am concerned with in the implementation of either, is if it will allow (a)
> "on the fly compression"; and (b) "on the fly encryption". Now, I am aware
> of software which operates on a file by file level to do either of those
> (gzip, or crypt (crude for encryption I know but a good example), but I am
> talking about encryption or compression on a filesystem level. I was told
> that using the loopback filesystem additional layers of filesystem can be
> added to yield these sorts of "on the fly" additions.
> Predicated on a choice of either JFS (XFS or ReiserFS, I know there
> is also ext3fs, but it doesn't really work yet I hear), what are the best
> methods to assure on the fly compression and also encryption of the highest
> order of magnitude.
None of these filesystems directly support encryption or compression, but they
can all use the loop device which does have some support for encryption at
least. Look at the manpage for losetup. There may be optional extensions to
the loop device for better encryption and compression, you will probably get
better answers by asking this question on the linux kernel mailing list.
One caveat on this is that the loop device pretends to be a block device under
the filesystem and talks to some underlying storage which is either a file,
or another block device. In the case of a file then the data coming out the
back end of the loop device is just written into that file's memory, and
flushing to disk is going to happen later. This will DESTROY the ordering
constraints required by journalling filesystems and probably result in
filesystems which are corrupted after recovery. I am not so sure what
happens with loop over a block device, but I would recommend you do extensive
testing before relying on something like this.
> Thank you for your time and consideration in advance.
> Very Respectfully,
> Stuart Blake Tener, IT3, USNR-R, N3GWG