Thanks for the info, John.

Is there anyone else in the bacula community with LTO3's seeing this 
behaviour?  I don't believe (but am not 100% sure) that I'm having any 
hardware-related issues.

Not sure what to make of this.  About 25% of tapes in a monthly run (70 
tapes) are under the 400Gb native, but then the other 75% are above it, 
some even hitting the 800Gb top.

Stephen



On 09/24/2012 12:02 PM, John Drescher wrote:
>> This is not likely a bacula questions, but in the chance that it is, or
>> the experience on this list, I figured I would ask.
>>
>> We've been using LTO3 tapes with bacula for a few years now.  Recently
>> I've noticed how variable our tape capacity it, ranging from 200-800 Gb.
>>    Is that strictly governed by the compressibility of the actual data
>> being backed up?  Or is there some chance that bacula isn't squeezing as
>> much onto my tapes as I would expect?
>>
>> 200Gb is not very much!
>
> These tapes are 400GB native. If you get substantially less than that
> you have a configuration problem (you set limits on the volume size or
> duration) or a hardware problem. Compression should be handled
> entirely and automatically by the tape drive. Bacula does not enable
> or disable hardware compression it just passes the data to the drive
> and writes as much as it can up until it hits its first hardware
> error. At that point bacula calls the tape full and verifies that it
> can read the last block. I believe if it can't read the last block
> this block will be the first block written on the next volume.
>
> John
>


-- 
Stephen Thompson               Berkeley Seismological Laboratory
stephen AT seismo.berkeley DOT edu    215 McCone Hall # 4760
404.538.7077 (phone)           University of California, Berkeley
510.643.5811 (fax)             Berkeley, CA 94720-4760

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