tapes cannot get full capacity

[dioworld]

Hi
I am using sony sdx2-50c ait drives, it suppose can hold 130gb compressed data, but on netbackp, i can see the full tapes gets about 98g of data, anyone knows how to get the full potential of the drives?

 

[comtec17]

This is due to files that cannot get compressed or if you have files that are not compressable being compressed in reverse (Meaning if you have a 1MB file that cannot be compressed might turn into a 1.3MB file).

 

[johnny99]

Almost anyone in the compression business is very optimistic when they look at how much they can compress.

On a high-end tapedrive you would often see average compression rates like this (but it depends on the data):

Mainframe: 1:4,0
Unix: 1:2,5
Windows: 1:1,5

I don't know anything about AIT drives but I would expect that it would be the same as DLT drives and they compress less then high-end drives.

 

[IThead]

Hi, I have a DLT8000 with 40/80GB density, but only get 36G max...

 

[PGPhantom]

If you bank on 1:1.5 compression, you are doing well and being fairly realistic. With 36Gb on a 40/80 tape a few things come to mind - Are you using software or hardware compression - Please tell me it is hardware!

If it is hardware, check your drive and make sure that you have selected the compression option, on DLT's there is a button on the left that allows you to select compression and a LED will light up when it is enabled.

If that has been verified and you are still only getting 36GB - What type of data is it? I have seen cases where the compression is actually 1:0.8 because the files being backed up were already compressed.