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BE 2010 R3 and compression - only 1.1 to 1

Posted by araczek 
BE 2010 R3 and compression - only 1.1 to 1
March 28, 2012 01:35PM
Hi,

Note I am just starting out with this whole backup setup so it does not have a track record yet.

First issue:
We have a NEO2000e tape library with an Ultrium 4 SCSI drive (user mode driver), I am using LTO3 tapes. Operating system is Server 2003. I have the "Enable compression" box ticked
on the tape device. When I do a backup (file types are typical desktop drivers, laptop drivers, printer drivers) I am only getting 1.1:1 compression. Drive is new and
tapes are new.

Second issue:
I click on one of the media and it tells me-
Used Capacity: 0 bytes of 390.9 GB
Available Capacity: 390.93 GB
Total capacity: 390.9 GB
Bytes Written: 1.5 GB

WHY is my tape AVAILABLE CAPACITY 390 GB ?? I understand compression relies on the type of data, data streaming speed
to drive, etc. But why would it show me just 400 GB (basically)? Wouldn't it show me ballpark 790 GB capacity IF compression
is on and working??

Driving me nuts. Don't want to eat up the small amount of tape media I have as it is.

...AR dazed and confused (for so long it's not true)
BE 2010 R3 and compression - only 1.1 to 1
March 28, 2012 01:52PM
I can't provide any info about the compression ratios as I'm more of a NetBackup admin but I think I can provide some insight into the capacity question.

BE can't assume what the compression ratio is going to be so it defaults back to telling you how much space the media has in native capacity. NetBackup does not even give you used capacities and total capacities. It will show you exactly how much data has been written to the media along with whether or not it is full. One has to manually calculate your compression ratios by dividing the written volume by the native capacity.

And as I write this, this could also explain why the compression ratios seem low. BE may not know how to properly calculate them until it starts writing beyond the native capacity. Once it starts that, then it should start showing higher compression ratios.
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