I just tried to create a sparse file in a tmpfs, and noticed that it
doesn't appear very sparse - quite dense in fact:

  euclid 57> df .
  Filesystem  1K-blocks      Used     Avail Capacity  Mounted on
  tmpfs          721740       324    721416     0%    /tmp
  euclid 58> dd if=/dev/zero of=foo bs=1 seek=99999999 count=1
  1+0 records in
  1+0 records out
  1 bytes transferred in 0.001 secs (1000 bytes/sec)
  euclid 59> df .
  Filesystem  1K-blocks      Used     Avail Capacity  Mounted on
  tmpfs          819396     97984    721412    11%    /tmp
  euclid 60> ls -ls foo
  97660 -rw-r--r--  1 simonb  wheel  100000000 Nov  9 23:35 foo

The same dd command on a 3.0 box with mfs /tmp shows this file:

  24 -rw-r--r--  1 simonb  wheel  100000000 Nov  9 23:36 foo

Simon.
--
Simon Burge                                   <simonb@wasabisystems.com>
NetBSD Development, Support and Service:   http://www.wasabisystems.com/