"+1 for @UnixGeek answer: deleting a file does not free up disk space until the process(es) with the file open are gone.
The ""standard"" tool to list open files is lsof -- I still don't think it's included with Solaris (it's been several years since I was a Solaris admin, or even used it), but is available from sunfreeware.
A quick google finds the Solaris utility pfiles can do something similar (but I haven't used it).
Also, fuser on the file name, but you need to check it before you delete the file(s). fuser is also useful for finding what has a port open, when a process tell's you it's already in use.
I will plug A Sysadmin's Unixersal Translator (ROSETTA STONE),
a very useful guide for anyone using multiple Unices and translating between them.
Bonus trick for recovering deleted files in /proc-based systems which are still open by a process:
cat /proc/<pid>/fd/<fd-of-delete-file> > recovered.data
I have used this in Linux, where ls -l /proc/<pid>/fd shows the initial file name (and [deleted]) in the output."
