Evan,

What OS, type of tape, type of drive, HW platform ?

I'm unfamiliar with a parameter to do what your asking
for for good measure, what version of Amanda ?

Actually, how did you determine that a drive within a changer
was shoe-shining ? What else shares the bus with the tape and
with the amanda work area drive(s) ?

On Wed, Dec 06, 2006 at 02:34:31PM -0600, Evan Harris wrote:
> 
> 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
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