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compression problem with external disk and tape

SFPandora
Level 4
My BE doesn't  seem to compress data: I tried to backup with compression some word files (300mb) both on external usb disk and on tape. The backup finished successfully but it didn't compress data. This happened with every compression option: software compression, hardware compression, no compression. Backup file has the same size.
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CraigV
Moderator
Moderator
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Hi,

It definitely depends on the file type...if the file is already in a compressed format, it will not compress again.
The only way to check is to see your report...it's going to have a backed up size, and a size on disk, but it won't do that for every file unless you have some sort of logging in place that is very in-depth.
The only way I know of is to check the tape and see what type of compression you got on the entire job.

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CraigV
Moderator
Moderator
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Hi SFP,

Some files cannot be compressed as they're already in a compressed format. No matter what sort of compression you take, that's as good as it will get. Zip files, certain image files etc. would be examples of files that won't compress at all.
Other files would, but the compression you would get is dependant on the files being backed up, and what your device is capable of. If you take an LTO3 tape, it's raw capacity is 400GB, while it's compressed capacity is 800GB. So it's 2:1, which is a best-guess scenario, and you will very seldom get it.
The best I can get is 1.5:1, but on other sites, the overall average is around 1.3:1.

Hope this helps?!?

SFPandora
Level 4
I don't think it can depend on the file type: I selected just .doc file created by Microsoft Word and they are usually quite compressible, and I can't get 1,5:1 but 1,1:1 and the backup size is exactly the same with software, hardware or no compression. Is there a way I can check if data are really compressed?

SFPandora
Level 4
I don't think it can depend on the file type: I selected just .doc file created by Microsoft Word and they are usually quite compressible, and I can't get 1,5:1 but 1,1:1 and the backup size is exactly the same with software, hardware or no compression. Is there a way I can check if data are really compressed?

CraigV
Moderator
Moderator
Partner    VIP    Accredited
Hi,

It definitely depends on the file type...if the file is already in a compressed format, it will not compress again.
The only way to check is to see your report...it's going to have a backed up size, and a size on disk, but it won't do that for every file unless you have some sort of logging in place that is very in-depth.
The only way I know of is to check the tape and see what type of compression you got on the entire job.

SFPandora
Level 4
yes but microsoft word files aren't compressibile? And is it possible that i backup 300 mb and backup size exactly 300mb?

CraigV
Moderator
Moderator
Partner    VIP    Accredited
Hi,
Well, if you have files that cannot compress which are sized at 300MB, they'd be backed up at 300MB as well.

Laters!