How to force amanda to serialize dumper/taper

[Evan Harris]

I'm having a problem with my tape drive shoe-shining because the holding 
disk can't keep up with the tape drive if it is also being written to by a 
dumper.  Without the extra disk seek overhead of dumpers writing to the 
holding disk at the same time, the holding disk should be plenty fast enough 
to keep the tape drive streaming.

Is there any way I can force amanda to serialize the dumper/taper so that 
they are never run concurrently?  I've already set inparallel to 1, but that 
only affects how many dumpers can run, not the taper.

I've also tried increasing the tapebufs parameter to 8000 (256MiB) to see if 
that would at least let the drive stay streaming for longer periods, but if 
it made any difference, it wasn't significant.  What thresholds does the 
taper use to decide when the tapebufs are filled enough to start tape 
motion?  There doesn't seem to be any docs on that, or settings to 
customize.

I did get a suggestion that I should just leave the tape out of the drive, 
let the dumpers fill the holding disk and then load the tape and run 
amflush, but that doesn't really work when using a changer, plus the holding 
disk isn't large enough for the total size of all the backups, though it can 
fit them one-by-one.

Seems like there should be a "speed" config option for holding disks like 
there is for network interfaces and tape drives, so that amanda could test 
to see if the holding disk can't handle dumpers using the holding disk at 
the same time a taper is running.  That seems like it'd solve the problem 
nicely, and even seems to fit with the scheme amanda uses for network 
interfaces.

Thanks.

Evan