Read-only ReiserFS support for FreeBSD 5.x

Xin LI delphij at frontfree.net
Tue Oct 19 12:20:00 PDT 2004


On Tue, Oct 19, 2004 at 09:40:47PM +0300, Kalev Lember wrote:
> One of the things I have missed in FreeBSD is a good journaling 
> filesystem. This is one of the places where Linux beats BSD: Linux 
> supports far more filesystems that the BSDs do.

From my view, journaling is not necessarily to be superior than the
SoftUpdates in FreeBSD, however, having journaling filesystem support
will make it possible for us to actually *compare* them and improve
our SoftUpdates implementation.  If you have found that some filesystems
outperform FreeBSD's, it might be because some other factors, and some
of these can be changed by tuning up the file system, while some others
lies on things other than journaling techniques.

> Writing a journaling filesystem from scratch is not a trivial thing to 
> do, however. Maybe we should consider using ReiserFS or some other 
> journaling one as FreeBSD's primary filesystem now that the 6-current is 
> branched?

I personally prefer SoftUpdates over Journalling because it guarantees that
everything written on disk is consistent while Journalling does not (you'd
say that it have transaction log and hence can rollback to a consistent
state, however in most journalling implementations this is not done in a
safe way so the reliability is in doubt).  To get journalling work in a
correct way you will need some non-violatile memory or UPS so the system
can guarantee its writes to the transaction log area is done correctly.

ReiserFS, however, *does* provide better performance when dealing with zillions
of small files.  I don't want to debate whether a well-designed system should
actually utilize this, but I believe it would be beneficial to bring some
different ideas we can take as reference :-)

> One of the issues with ReiserFS is the licence of course.
Yes for sure, and with this in concern it would not be possible for us to
make it a part of kernel before someone actually re-write it from scratch.

My intention is, however, to write a new (or to improve our existing)
filesystem which is optimized for large files (e.g. databases), while
providing "fairly good" performance when dealing with many small files.

Cheers,
-- 
Xin LI <delphij frontfree net>	http://www.delphij.net/
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