freebsd-performance Digest, Vol 3, Issue

Michael Nottebrock michaelnottebrock at
Thu May 1 19:08:44 PDT 2003

On Friday 02 May 2003 03:17, randall ehren wrote:
> what do you mean by "set their free reserve"?

A lot of FreeBSD users only realize the existance of this when they are faced 
with a situation described in the FreeBSD FAQ:


9.25. How is it possible for a partition to be more than 100% full?

A portion of each UFS partition (8%, by default) is reserved for use by the 
operating system and the root user. df(1) does not count that space when 
calculating the Capacity column, so it can exceed 100%. Also, you'll notice 
that the Blocks column is always greater than the sum of the Used and Avail 
columns, usually by a factor of 8%.

For more details, look up the -m option in tunefs(8).


... which says:


From the tunefs(8) manpage:

     -m minfree
             Specify the percentage of space held back from normal users; the
             minimum free space threshold.  The default value used is 8%.
             This value can be set to zero, however up to a factor of three in
             throughput will be lost over the performance obtained at a 10%
             threshold.  Settings of 5% and less force space optimization to
             always be used which will greatly increase the overhead for file
             writes.  Note that if the value is raised above the current usage
             level, users will be unable to allocate files until enough files
             have been deleted to get under the higher threshold.


	Michael Nottebrock
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