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Why can't I store 705GB on a 400GB/800GB LTO-3?

New Member

Why can't I store 705GB on a 400GB/800GB LTO-3?

I am having a problem understanding how much data I can back up. My tape is ejected as it it is full when to me it seems under capacity.


What confuses me is that none of the sizes I see are consistant.




Selected            1930347 objects, 705.53 GB

Completed        1727844 objects, 567.97 GB (81%)

Not attempted   202503 objects, 137.55 GB (19%)


Media type  LTO-3 400GB/800GB

Compression ratio:  0.9:1

Native total capacity:  390.92 GB

Native remaining capacity:  1.31 GB


Can anyone explain to me how 567.97GB fits in 390GB? I assumed it would work to the upper limit of 800GB?

Occasional Contributor

Re: Why can't I store 705GB on a 400GB/800GB LTO-3?

I'm not sure what Backup software you are using, or whether you are using hardware or software compression, but this link should help you understand more.



Honored Contributor

Re: Why can't I store 705GB on a 400GB/800GB LTO-3?

It would be interesting to see what L&TT reports in a support ticket.  That would be the information as seen by the drive.  That will show you whether the drive is actually configured to compress or not and report the compression ratio achieved by the drive based on the data recieved.


The number reported below sounds suspiciously like uncompressed.  For the difference in sizes it is possible that one number is based on the size on disk and the other number is based on the actual size of the files.  That difference seems a bit large but those two numbers are always different for disks but not so much for tapes.   On disks each file uses a number of logical blocks each with a fixed size so there is a little unused space with every file.  On tape the files can be end-to-end and use almost exactly the file size (some variation depending on fixed or variable block sizes and how the application packs data).