Critical problems with md on 5.0-RC1

[Jacques Garrigue]

There is a very serious problem in the md filesystem, since at least
5.0-RELEASE, and it is not yet fixed.

You can see details of the problem at

    http://www.freebsd.org/cgi/query-pr.cgi?pr=47538

Since this problem may result in data corruption, I believe that at
least there should be a warning in the release notes about NOT using a md
filesystem for /tmp. Lots of people seem to do that.

Short description (assuming 256M of machine memory, and about 230M of
data in /usr/X11R6/lib):
      mdmfs -s256M /dev/md0 /mnt
      tar cf - -C /usr/X11R6 | tar xf - -C /mnt
      diff -r /usr/X11R6/lib /mnt/lib
And you start seeing the differences...
Apparently some sectors are just zeroed. File size does not change.
Pretty hard to detect.

Anothere problem I have is that md on a vnode in an msdos partition
doesn't work. I have been using it to get extra disk space on a
laptop.  In 5.0-RELEASE the system just froze, now the file system
starts refusing to sync while unpacking a big archive with unzip.

As a conclusion, two of my favorite features since FreeBSD-2.2, namely
memfs and vn, are currently broken. I suppose that one has to wait a
bit after an hostile takeover :-)

Cheers,

---------------------------------------------------------------------------
Jacques Garrigue      Kyoto University     garrigue at kurims.kyoto-u.ac.jp
		<A HREF=http://wwwfun.kurims.kyoto-u.ac.jp/~garrigue/>JG</A>