Compressing Backup to 40/80 DLT IV Tape

[gvnw-chuck]

Lately, I have been backing up my data and it usually requires 2 DLT 40/80 GB tapes instead of 1 tape.  Before I was able to backup about 50 GB of data on one tape, but now when I backup up the data its backing up 67 GB of data and it gets 60 GB on one tape then I have to swap out another tape for the remaining data.

How can I utilize the full 80 GB on one tape?  It doesnt make sense to me that I can get 60GB but the remaining 7 GB goes on the other. Such a waste of tape.

Here are my specs:

DLT TAPE IV
40GB Native 80 GB Compressed

Windows Server 2000 SP4
Backup 12.5

Devices:Properties:Configuration:
Enable Compression:Checked
Block Sie (Per Device) 64 KB
Buffer Size (Per Device) 64 KB
Buffer Count:10
High Water Count:0

Write Single Block Mode:Checked
Write SCSI pass through mode: Checked

Job Setup:Properties:Settings:General
Backup Method: Full - Using Archive Bit (reset archive bit)

Verify after backup completes:Checked
Compression Type:
Harware (If available, otherwise none)

I appreciate any insight on how I can get this to backup on one tape instead of two.

[Ken_Putnam]

2:1 compression is Marketing Hype, not Engineering Promise.  Some data compresses  very well, some not very well at all

If you can get 60GB on a DLT IV tape, you are getting 1.5:1 compression, which is not bad at all.  I generally use 1.2-1.3:1 as a rule of thumb until a particular backup has run several times to get an real-world average,

See http://www.symantec.com/docs/TECH6076
 

[pkh · Accepted solution]

On the subject of compression, you might want to read my article

https://www-secure.symantec.com/connect/articles/compression-short-explanation