I needed to add more disk space to my CentOS VM, so I added another virtual disk, then used lvextend to add the space to the existing partition.

The steps I followed was:

echo "- - -" > /sys/class/scsi_host/host0/scan
pvcreate /dev/sdb
vgextend VolGroup00 /dev/sdb
lvextend -l +100%FREE /dev/VolGroup00/LogVol00
resize2fs /dev/VolGroup00/LogVol00

This worked fine. I subsequently filled up the VM, then deleted most of the used disk space. However, the unused disk space was never recovered after I deleted all of the files.

This will illustrate what I'm saying better:

# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                       61G   32G   26G  56% /
/dev/sda1              99M   20M   75M  21% /boot
tmpfs                1006M     0 1006M   0% /dev/shm

# pwd; du -h --max-depth=0
/
5.1G    .

I cannot figure out how to get the partition to see that only 5.1 GB is used. Any ideas what I'm doing wrong?