Zitat von lst_hoe02 AT kwsoft DOT de:

> Zitat von Nils Juergens <nils+bacula AT muon DOT de>:
>
>> Hello Andreas,
>>
>> Am 20.08.2012 17:29, schrieb lst_hoe02 AT kwsoft DOT de:> As the tape is
>> altering speed all the time with Bacula i would like to
>>> know if there is a possibility to get closer to the dd values and what
>>> could be the bottleneck in such a setup?
>>
>> for me (with LTO-3) increasing Maximum block size has had quite the
>> impact on performance.
>>
>> Sadly, with the new setting I had trouble reading my tapes so switched
>> back to the old configuration.
>>
>> I suspect you may get around the problem if you re-label all your tapes
>> after switching the block size, however I have not testet this. Maybe
>> someone can shed some light on the whole block size business? :-)
>
> Would really nice indeed. As far as i understand the block size used
> as default (and max.) if nothing is specified is 64,512 Bytes. This
> looks a little bit low for high-speed tape and i'm not sure what the
> downside of higher values could be or why the manual state that there
> is no need to set it explicit (higher).
> As i'm in the testing phase i will have a look if higher values lead
> to any trouble. Anyone aware why the default of 126*512 Bytes was
> choosen?
>

Some short tests with the "Maximum Block Size" set, show transfer  
speed to the LTO-4 of 87MBytes/sec with 256K and 98MBytes/sec with 1M  
with Bacula encrypted data, so with this we are reaching the  
theoretical uncompressed speed of the LTO-4 device by ~20%.
It would be really helpful if there is some developer to say if there  
is any downside of large block sizes?

Regards

Andreas


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