On Tue, Nov 15, 2005 at 02:50:17PM +0000, Rodrigo Ventura wrote:
> 
> What exactlty means the "sleep" configuration parameter in the
> changer.conf file? I notice some lag in the tape commands (it seems
> the tape is doing nothing, and the amtape is just sleeping...), so
> maybe the default value of 90 is too conservative for my system. How
> can I safely tune it?

Honestly, the only way is reduce it and see if it causes problems.

If I were to try and "measure" what might be needed, I'd position
a tape about 'half unwound' (fun to try and figure that out on
serpentine tape formats :)  Then I'd type in a rewind with mt,
and while it was rewinding, but before you get a shell prompt,
enter another tape command, say a dd for a gigabyte to /dev/null.
But don't hit the enter key on the dd command until you see the
prompt return from the mt command.  Probably when the prompt
appears, the tape will actually still be rewinding.  However,
immediately upon seeing the prompt hit the return key and notice
how long it takes the tape to begin moving forward.

Some drivers would give an error to status requests during this 
period between the apparent command completion and the actual
"drive ready" condition.  This is the delay for which chg-scsi
is trying to accomodate.  If dd receives an error, keep repeating
the dd command until it does work.

As a fudge factor, I'd double your measured delay.

-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
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