Thomas Mueller schrieb:
> 
> >> > 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. 

That's strange. Bacula shouldn't stop writing, if the Max File Size is
reached it writes a EOF marker and then continuous writing to the next
file. Have you activated attribute spooling? Bacula should then only
write to the DB at the end of a job.

I've never used iotop but with dstat I see a more or less constant
stream from the spool disks to the tape drive. 

If this is an HP drive, I would start with the HP LTT tool and a Media
and Drive Assessment Test. There is also an performance test. This
helped me several times to identify bad drives or tapes.

http://h18000.www1.hp.com/products/storageworks/ltt/index.html

There are only RPMs for linux, but with alien you can generate a deb
package for debian if you need. I run the tests in CLF mode (command
line).



Ralf

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