Anyone who followed the original thread "tape read errors" started 3/3/2008 may 
be 
interested in this followup.  I did a bit of testing with a variation of the 
mtx-changer script on my VXA-320 Autoloader and noted that the time between a 
successful load of a tape into the drive and when the "mx status" command 
returned 
"ONLINE" varies tremendously.  It is sometimes about 30 sec.  It is often about 
3 
min.  Sometimes it is as much as 17 min.

I spoke to support at Exabyte to see if they could explain this.  It is 
expected 
behavior. In fact, he told me that 20-30 min would not be unexpected.  The 
drive 
firmware is paranoid about the integrity of the system area on the tape 
(normally 
written at the very beginning).  Whenever the drive passes over the system area 
(it 
happens when tapes are loaded) it takes the opportunity to do some diagnostics. 
 If 
it has trouble reading the data there it will try several more times.  
Sometimes it 
will decide that the area is wearing or unreliable and it will move the system 
data 
to a blank section of tape farther away from the beginning.  It may decide to 
re-tension the tape.  When a tape is written to the end of tape, it will put 
another 
copy of the system data there.  All of this means that the drive can spend a 
fair 
amount of time convincing itself that all is well with the newly inserted tape. 
After it is convinced, it will return ONLINE in response to a status query.

I guess this paranoia on the part of the firmware is a good thing as it 
improves 
reliability.  In order to get bacula to gracefully handle the long wait I set

Maximum Changer Wait = 1800  #(30 minutes)

in the device resource and I modified the mtx-changer script to query for the 
status 
at 10 sec intervals to a max of 28 minutes.

Mark Nienberg


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