Hi,

On 19/04/2013, at 9:02 AM, gunnerjoe <networker-forum AT BACKUPCENTRAL DOT COM> 
wrote:

> Hello,
> 
> I checked all the logs there are no errors at all except an occasional "ASR" 
> could not back, but nothing that would explain why most tapes reach "Full" at 
> 2.5 - 2.7 TB and one tape reported full at 1800 GB. 
> 
> Even 2.5 TB per tape is annoying as that is 500 GB short of what LTO 5 tape 
> is suppose to hold (3TB).

No. No, no, no. LTO 5 is NOT supposed to hold 3TB.

An LTO 5 tape is supposed to hold 1.5TB.

Vendors and the LTO consortium quote a 2:1 compression ratio for tapes, but 
this is entirely up to the data you have.

Your data explains why you're not getting 3TB onto a tape. Not all your data - 
in fact, the majority of it, is clearly not compressible to a 2:1 compression 
ratio. And sometimes you'll hit data which is compressible to far less a degree 
by that again.

If you're planning for tape media utilisation and you haven't done a full data 
review of the environment or don't have very specific types of data, you should 
be planning for a 1.2:1 or 1.3:1 compression ratio -at most- for an environment.

Cheers,
Preston.