There is a file system and there isn't actually 20 GB of disk space in there.

/dev/sdb1 20G 17G 1.9G 91% /var/tomcat

when I do a du -sh on /var/tomcat I only get:
du -sh
312M .

The file system keeps running out of space.
Does any one know whats happening?

vgscan:

Reading all physical volumes. This may take a while...
Found volume group "vg00" using metadata type lvm2


--- Volume group ---
VG Name vg00
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 9
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 8
Open LV 8
Max PV 0
Cur PV 1
Act PV 1
VG Size 19.88 GB
PE Size 32.00 MB
Total PE 636
Alloc PE / Size 636 / 19.88 GB
Free PE / Size 0 / 0
VG UUID 2cAcZd-cvD4-3Wl2-tdNl-2Fkn-MqpB-7SFTtG

--- Physical volume ---
PV Name /dev/sda2
VG Name vg00
PV Size 19.89 GB / not usable 19.49 MB
Allocatable yes (but full)
PE Size (KByte) 32768
Total PE 636
Free PE 0
Allocated PE 636
PV UUID f7LuT2-MqJI-npun-uk4A-EdhK-Vna2-rj3bZK

So your problem is that "df" is showing 17G used and "du" is only showing 300M?

This happens when there are files still held open by processes, but that have been deleted.

Assuming that only Tomcat is using /var/tomcat, and restart of Tomcat should clear it up. As a last resort, a reboot should clear it up. If even a reboot doesn't fix it, then you should unmount /var/tomcat (perhaps in single user mode) and fsck it.

Yes the answer to your question about the different size in the file system /var/tomcat.
Thanks let me look into this.