What things should I check to confirm that compression is actually happening on our tape backup system? Although the tapes are marked as 200G/520G (native/compressed) capacity, they seem to fill up before the 200G mark (some less than 100G).
- Sony AIT-4 tape autochanger
- Sony SDX4-200C (AIT-4) tapes
- Ubuntu Lucid
I've tried checking hardware compression with: tapeinfo -f /dev/nst0, which gives
Product Type: Tape Drive Vendor ID: 'SONY ' Product ID: 'SDX-900V ' Revision: '0102' Attached Changer API: No SerialNumber: '0001000036' MinBlock: 2 MaxBlock: 8388608 SCSI ID: 1 SCSI LUN: 0 Ready: yes BufferedMode: yes Medium Type: Not Loaded Density Code: 0x33 BlockSize: 0 DataCompEnabled: yes DataCompCapable: yes DataDeCompEnabled: yes CompType: 0x3 DeCompType: 0x3 BOP: yes Block Position: 0 Partition 0 Remaining Kbytes: 201778000 Partition 0 Size in Kbytes: 201779000 ActivePartition: 0 EarlyWarningSize: 0 NumPartitions: 0 MaxPartitions: 0
... so I presume it's on.
- The Bacula documentation says hardware compression needs to be enable with "system tools such as mt"
- The data "should" compress well. The largest proportion is text files with lots of redundancy (genomic data). bzip often reduces to 10-30%
- I have compression (i.e. software compression) turned off in Bacula