A "softupdates" problem?

[Mark]

Hello,

Making a daily server backup, using dump (FreeBSD 4.7R), I keep running into
a "softupdates" problem. That is, prior to backing up a partition (/var), I
move a large file (several gigabytes) off that partition. But because of the
"softupdates" effect, the size of that large file is added to the dump-file
size, as if it were still on the partition!

I have been able to circumvent that, in the past, by waiting a few minutes
before starting the dump (until df reflects the correct size). This is not
really ideal, though, as I disallow outside connections while in backup (so
as not to change the /var partion with log-files being filled and such). Is
there not a command to force 'softupdates' to write out its cache
immediately?

Much obliged,

- Mark