Compression Ratio for ADIC DLT 7000

[webstorm]

I have a NT 4.0 system with AS 6.x loaded and an ADIC DLT 7 tape cartridge, all which are running well. Hardware compression is enabled, software compression is disabled in AS. I am currently using Fujifilm DLT IV tapes, in 2002, I was using the ADIC tapes.
Every week when I do the full backup for 70GB of data (Acad DWG data), I need to use two tapes to complete the full backup. When I go into the AS log, it says that it was able to fit 53GB on one tape. Ideally I am supposed to be able to fit 70GB compressed on each of those tapes, or 35 GB uncompressed (native). At least this is what the tapes I use tell me. Is this just the ideal compression ratio achieved with one type of data in a laboratory? Right now, the compression ratio I am achieving is running at 1:1.5, and has been doing so ever since I started managing this system. I know that DWG's are very compressible, so why we can't get higher that 1:1.5 is puzzling me.

Joe

 

[TheLad]

The advertised tape capacity is 35/70Gb but in essence this is not always true.

For an example, take Winzip - when you zip a file up, the file does not zip to 1/2 the size. Likewise when a DLT compresses files, depending on what the files are, it is not always possible to compress them as much as advertised.

It all depends on the type of files you are backing up as well. For example, JPG files do not compress well as they are effectively already compressed to a small size. Databases may contain "white space" so threfore may compress more. -----------------------------------------------------
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