DLT tape problems with BE8.0

[montigue]

I'm using BE 8.0 on an NT4 Server to backup all my critical files. The total size of all my critial files is approximately 55GB. Im using DLT IV catridges which I know can hold 70GB (2:1)compressed. Unfortunately, my full backups get to 38GB and a request for scratch media comes up. I have verified that the backup is compressing the data. The tapes I am using were previously part of an old media set and were erased. Could these tapes be the reason why my backups are not fitting on one DLT tape.

 

[jamkey]

Keep in mind the 2:1 compression ratio is theoretical in nature. It assumes the average compressability of the files in question in 50%. However, in my experience its closer to only 25%. Therefore 100gb of data would compress down to about 75gb not 50gb. If the data is MORE compressible (like text files or Access database files) then you would actually get better than this. Exchange Information stores are also highly compressible. To see what kind of compression rate is possible with the backup set in question temporarily change from hardware compression to software compression for the job(s). This will show for each set (c$, d$, etc.) what kind of compression ratio was obtained. You will probably see something like an average of 1.1:1 or 1.2:1 based on how much you are able to get to tape. I wouldn't recommend staying w/ Software compression though b/c it will not let you restore the data with any other application like NT backup which is useful if you are taking the tape where you don't have Backup Exec installed; plus, Software compression is more CPU intensive (not too much though). But I have seen cases where Software compression does better than hardware (which of course will vary w/ the h/w) in both capacity and speed.