Dear bacula insiders,
I got a replacement for my old DDS5 - a LTO4.
Setup is D2D2T.
The problem is not the setup, but the tape drive utilization.
The disk-storage can provide well over 300MByte/s, and using tar with -b
126 or dump or dd, I see 78-160MB/s moving to the drive. So the problem
is probably not hardware related.
When I have bacula copying a job to tape, there are very often outages,
weher no data at all is transfered to the tape.
I found out that after this break, the `mt status` reports a incremented
file number. When does bacula write a new file, meaning why so often?
I'd like to treat my tape drive as gently as possible, so the job result
of a average transfer rate of 65MB/s makes me worrying about massive
repositioning.
Can I optimize my setup so that there won't be so many new files written
on tape? Or should the creation of a new file mark been done without
interruption of the transfer, and there's something wrong with my setup?
Another strange thing for me is the device utilization. When using tar I
can see a %busy report of ~90 constantly for the tape device, no matter
if the transferrate is 80MB/s or (due to compressable material) 120MB/s.
When bacula writes 75MB/s, I get only 68% busy reported ?!? Up to the
break point (new file), after which I get 350% usage.... And if
compression allows 100MB/s the %busy rate decreases to 50!?!
But this is probably OS-specific (FreeBSD), just in case someone could
enlighten me why this is not the case with other tape writers...
Thanks ins advance,
-Harry
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