I've had this problem before and I think only a reboot solves it. In a nutshell when I delete a file, I don't see the space when I do a df -h. This time, I was creating a jail and doing the buildworld when I noticed I only had less than 900 megs. I deleted an iso that was 1.2 Gigs but it doesn't show. I am using zfs on root. Any, suggestions.
Code:
[14-04-24 11:16]root@/home/larry#uname -a
FreeBSD freebsd.webbrews.com 10.0-RELEASE-p1 FreeBSD 10.0-RELEASE-p1 #0: Tue Apr 8 06:45:06 UTC 2014 root@amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC amd64