FFS_SOFTUPDATES(4)        OpenBSD Programmer's Manual       FFS_SOFTUPDATES(4)

NAME
     ffs_softupdates

DESCRIPTION
     The FFS_SOFTUPDATES kernel config option enables a scheme that uses par-
     tial ordering of buffer cache operations to allow metadata updates in the
     fast filesystem to happen asynchronously, increasing write performance
     significantly.  Normally, the ffs filesystem writes metadata updates syn-
     chronously which exacts a performance penalty in favor of filesystem in-
     tegrity.  With soft updates, you gain the performance of asynchronous
     writes while retaining the safety of synchronous metadata updates.

     Soft Updates must be enabled on a per-filesystem basis.  To do this, boot
     into single user mode and run ``tunefs -s enable special'' on each char-
     acter special disk device you want to enable soft updates on, then run
     ``reboot -n''.

CAVEATS
     Soft updates should be considered experimental at this time.
     There should be a mount(2) option to enable soft updates.
     The current license for ffs_softupdates is more restrictive than the rest
     of the OpenBSD kernel; this will be changed at a future date.

AUTHOR
     Marshall Kirk McKusick

LICENSE
     The following are the copyrights and redistribution conditions that apply
     to this copy of the soft update software. For a license to use, redis-
     tribute or sell the soft update software under conditions other than
     those described here, please contact the author at one of the following
     addresses:

           Marshall Kirk McKusick          mckusick@mckusick.com
           1614 Oxford Street              +1-510-843-9542
           Berkeley, CA 94709-1608
           USA

     Redistribution and use in source and binary forms, with or without modi-
     fication, are permitted provided that the following conditions are met:

     1.   Redistributions of source code must retain the above copyright no-
          tice, this list of conditions and the following disclaimer.

     2.   Redistributions in binary form must reproduce the above copyright
          notice, this list of conditions and the following disclaimer in the
          documentation and/or other materials provided with the distribution.

     3.   None of the names of McKusick, Ganger, Patt, or the University of
          Michigan may be used to endorse or promote products derived from
          this software without specific prior written permission.

     4.   Redistributions in any form must be accompanied by information on
          how to obtain complete source code for any accompanying software
          that uses this software. This source code must either be included in
          the distribution or be available for no more than the cost of dis-
          tribution plus a nominal fee, and must be freely redistributable un-
          der reasonable conditions. For an executable file, complete source
          code means the source code for all modules it contains.  It does not
          mean source code for modules or files that typically accompany the
          operating system on which the executable file runs, e.g., standard
          library modules or system header files.

     THIS SOFTWARE IS PROVIDED BY MARSHALL KIRK MCKUSICK ``AS IS'' AND ANY EX-
     PRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
     WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
     DISCLAIMED.  IN NO EVENT SHALL MARSHALL KIRK MCKUSICK BE LIABLE FOR ANY
     DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAM-
     AGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
     SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEV-
     ER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LI-
     ABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.

SEE ALSO
     fs(5),  config(8),  sysctl(8),  tunefs(8).

     Marshall Kirk McKusick, William N. Joy, Samuel J. Leffler, and Robert S.
     Fabry, A Fast Filesystem for UNIX.

     Gregory R. Ganger, and Yale N. Patt, Soft Updates: A Solution to the
     Metadata Update Problem in File Systems, CSE-TR-254-95.
     http://www.ece.cmu.edu/~ganger/papers/CSE-TR-254-95/

OpenBSD 2.6                     March 15, 1998                               2
