>> > With
>> > 
>> > Maximum File Size = 5G
>> > Maximum Block Size = 262144
>> > Maximum Network Buffer Size = 262144
>> > 
>> > I get up to 150M MB/s while despooling to LTO-4 drives. Maximum File
>> > Size gave me some extra MB/s, I think it's as important as the
>> > Maximum Block Size.
>> > 
>> > 
>> thanks for providing this hints. just searching why my lto-4 is writing
>> just at 40mb/s. will try them out!
>> 
>> searching the "Maximum File Size" in the manual I found this:
>> 
>> If you are configuring an LTO-3 or LTO-4 tape, you probably will want
>> to set the Maximum File Size to 2GB to avoid making the drive stop to
>> write an EOF mark.
>> 
>> maybe this is the reason for the "extra mb/s".
> 
> Modifying the Maximum Block Size to more than 262144 didn't change much
> here. But changing the File Size did. Much.

I found a post from Kern saying that Quantum told him, that about 262144 
is the best blocksize - increasing it would increase error rate too. 

> 
> Anyway, 40 MB/s seems a bit low, even with the defaults. Before tuning
> our setup I got ~75 MB/s. Are you spooling the data to disk or writing
> directly to tape?

yes, i was surprised too that it is that slow. 

I'm spooling to disk first (2x 1TB disk as RAID0, dedicated to bacula for 
spooling). i will also start a sequential read test to check if the disks 
are the bottleneck. The slow job was the only one running.

watching iotop i saw the "maximum file size" problem: it stops writing 
after 1 GB (default file size) and writes to the DB and then continues 
writing. so for a LTO-4 it stops nearly 800 times until the tape is full. 


- Thomas


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