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 � 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
>>> [EMAIL PROTECTED] 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 <[EMAIL PROTECTED]>
Sent by: "ADSM: Dist Stor Manager" <[EMAIL PROTECTED]>
10/24/03 06:58 AM
Please respond to "ADSM: Dist Stor Manager"
To: [EMAIL PROTECTED]
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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