We have a NW6.5sp4a cluster with an ultrium2 tape library attached. We run Arcserve 11.1 for backup but we have a problem in that when a backup runs it will decompress all the files, the volume that has a problem with this is 300Gb in size with 2000000 files both large and small and many directories.
There is only 12Gb of space left on the volume with 9Gb of compressed space and 20Gb space saved by compression.
When we do a full backup the volume will run out of space, but after the backup it will recompress the file and we will end up with 12Gb free space again.

Has anyone any ideas?

The volume is NSS and from the compression screen you can see the files uncompressing when the backup runs. I have also checked in the backup job that it keeps the files compressed.