Managing Cartridge Sizes with ProtecTIER

 

Problem(Abstract)

With Virtual Tape Libraries the total amount of space is often variable, and can make managing cartridges complex. This technote is intended to enhance the User Guide and help administratrors to plan and manage their ProtecTIER cartridges and repsitory

Symptom

Unable to determine how many scratch tapes or free space is available. Also Cartridges may be marked full before expected.

Cause

The ProtecTIER repository is estimated while it is empty, and the actual results may be different then planned. Changes in the environment also can affect the planning.

Environment

All ProtecTIER VTL systems

Diagnosing the problem

If cartridges are showing full on the ProtecTIER manager GUI, before they reach the planned size.

Resolving the problem

ProtecTIER Tape Capacity

All Cartridges will get an equal amount of space up to either the LIMIT that is
configured when created, or the calculated amount of Nominal Space / Number of Carts.

Once a Tape is “FULL” and Early warning is sent to the backup application, the tape
will be removed from the calculation of “Number of Carts” This allows the system to
adjust the size of the remaining (Non-FULL) tapes to use use the Nominal space effectively

If the Nominal space is not big enough to hold the total of “Number of Carts” * “LIMIT size” of the cart then, those tapes will be marked FULL before they reach their size (aka, no thin provisioning)

Knowing this behavior can help an administrator know when it is best to add more
cartridges as well as if it is best to Limit the size of the carts, or leave them unlimited.

IBM recommends to leave the carts unlimited in MOST cases.
In some cases, you can limit the size, to allow you to reserve space, or divide space
in libraries

Example: Two Libraries with 500 carts and 1000 carts. – your utilization will be 33% for the
smaller Library, and 66% for the larger

Deciding how many carts should be based on the Nominal space in the repository and either
calculated to have a desired aproximate size (Unlimited) or Calculated to all enough space
for all carts to reach the limit that is set while leaving a little room for fluctuation the factoring
ratio

Some Cases where Cartridge size has led to problems:

1.) Low Scratch tapes result in thinking that adding scratch tapes at limited size will bring
more space to the Backup Application . This will work, if there is a reserve of nominal
space in the repository. However, if the Factoring Ratio is lower then planned, and resulting
in less space, adding carts will tend to result in even smaller cartridge size.

2.) Insufficient idle time for Background jobs result in buildup of Delete and Defrag Data,
reducing Allocable space for Backups. Adding Cartridge in this scenario also can reduce the
size of the cartridges, having negative impact.
(see this Technote for MRC monitoring/tuning)

3.) Extra Library with 1000 extra empty tapes, result in Production Library to run out of room even
though the Repository showed plenty of nominal space. Adding tapes in this case results in
even smaller tapes as well.

4.) Collocation of backups with many partial tapes may make the Repository appear to have
lots of space, but the partial tapes consume more then expected due to size and use
In this case, Limiting the tapes to smaller size could have helped. Allowing them to store
more efficiently

Finally, If the repository had more space available when you multiply total tapes by
the amount of space, then it is a good plan to add more limited cartridges. (this wont happen
if you dont have any limited size tapes) –

Note, if you make a mixture of tapes sizes and types, it will be very complicated. If you want
to unlimit all of your existing tapes it can be done by IBM support. Contact IBM support and
request help with running the support utility to unlimit the cartridge size.

Get the Cartridge Whitepaper here

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