As I understand it, the gripper is most often used when there is a request load 
a tape into a drive which already has a tape in it (or maybe an unload pending).

The sequence is load new tape into gripper 1, move to drive, remove tape into 
gripper 2, load drive from gripper 1, put away gripper 2.

I have a library with 3 sections and 4 drives.  I use as many drives as 
possible at peak times. If there is a free drive available, TSM (4.2) will 
always load a new mount into an idle drive if one is available, thus defeating 
the use of the dual gripper.  TSM also seems mostly to make requests of the 
robot sequentially, so that even in cases where one would think the dual 
gripper could be used it is not.

My stat is less than 1% of mounts using the second gripper.  On the plus side, 
we had an intermittent problem with one gripper not putting carts away 
properly,  eventually the accessor arm would run up against the cart that was 
not properly in its slot, the breakers would go and an engineer visit was 
required to reset them.  The work-around for this was to disable the gripper 
with the problem.

Now that the gripper problem is fixed (finally - it took 2 ½ years of 
intermittent problems), we were seriously considering downgrading to a single 
gripper to get that extra 10% capacity, but have decided now to go to 3592 
instead.

BTW, the reason that it is acceptable that the IO port has the top two slots 
unavailable when gripper 1 is down is that you can simply load it with reduced 
capacity in such a case.  Capacity is affected but not function.  On the other 
hand, for a normal slot, it would be unacceptable to most users that 1 in 20 
loads would fail if one of the grippers failed.

Steve Harris
Queensland Health, Brisbane Australia

>>> allen.barth AT DB DOT COM 25/10/2003 5:24:10 >>>
Our dual gripper is used 6% of the time, but we also have an HA setup (2
accessors) which requires dual grippers.  You do lose storage slots at the
top and bottom as noted, but the thing I don't understand is why the top 2
slots of the I/O door aren't blocked out like the shelves because the
bottom gripper can't reach these either.

Just one of those odd observations.

-Al





Richard Foster <Richard.Foster AT HYDRO DOT COM>
Sent by: "ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU>
10/24/03 06:58 AM
Please respond to "ADSM: Dist Stor Manager"


        To:     ADSM-L AT VM.MARIST DOT EDU 
        cc:
        Subject:        Re: 3494 Library and dual gripper?



> A dual gripper shaves some seconds off the overall time.

It may be worth pointing out that a dual gripper loses you some library
tape slots - 10% of them, in fact. The upper gripper cannot reach the
lowest 2 slot levels, nor can the lower gripper reach the highest 2
levels.
Therefore these 4 levels are lost (and are physically blanked off in our
library).

It's an open question why IBM chose to do it that way, because it was
surely possible to program the control PC to use the appropriate gripper
for these levels. Probably that nice warm feeling of redundancy.

Richard Foster




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