Managing cartridge sizes with ProtecTIER
This appendix provides general information about managing cartridge sizes with ProtecTIER. With ProtecTIER, the total amount of space that is available in your repository is variable. These dynamics can make managing cartridges complex. This appendix is intended to help administrators to plan and manage their ProtecTIER cartridges and repository.
This appendix describes the following topics:
Effects of dynamic cartridge sizes
In a long running ProtecTIER environment, the HyperFactor ratio tends to stabilize around a certain value. If you then encounter changes in your environment, these changes have an unexpected effect on the HyperFactor ratio. When the HyperFactor ratio changes, the amount of free space that is available in your repository is recalculated. A higher HyperFactor ratio results in more free space being available. A lower HyperFactor ratio results in less free space being available.
After such events, you might find difficulty in determining how much free space is available. Also, you might see virtual cartridges that are marked as full before such an event is expected.
The mechanism behind fluctuating cartridge sizes
All virtual cartridges get an equal amount of space up to either the LIMIT size that is configured when the virtual cartridge was created (maximum cartridge size), or the calculated amount of Nominal Space/Number of Carts.
If the nominal space is not large enough to hold the total of Number of Carts times the LIMIT size of the cart, then those tapes are marked full before they reach their size (that is, there is no thin provisioning).
Knowing this behavior can help an administrator know when best to add more cartridges and whether to limit the size of the carts or leave them unlimited.
Deciding on a limit for the virtual cartridge size enables you to reserve space or divide space in libraries. With this strategy, you can prevent one of your virtual libraries from using up all the space in your repository, causing the other libraries to run out of space.
For example, if you have two libraries, one with 500 carts and the other with 1000 carts, your usage is 33% for the smaller library, and 66% for the larger library.
The decision about how many carts you have should be based on the nominal space in the repository. The number of carts should be either calculated for a wanted approximate size (unlimited) or calculated so that there is enough space for all carts to reach the limit that is set, while leaving a little room for fluctuation (the factoring ratio).
Having the wrong cartridge size has led to problems in the following cases:
•You might think that because you have low scratch tapes that adding scratch tapes at a limited size brings more space to the backup application. This situation works if there is a reserve of nominal space in the repository. However, if the factoring ratio is lower than planned, and less space results, adding cartridges results in an even smaller cartridge size.
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Important: Adding more virtual cartridges does not increase the available free space in your repository. If you face an out-of-space condition, you must expand your ProtecTIER repository by adding more physical disk to the back end.
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•An insufficient idle time for background jobs results in a build-up of delete and defragmentation data, which reduces allocatable space for backups. Adding cartridges in this scenario can reduce the size of the cartridges, which has a negative effect.
•An extra library with 1000 extra empty tapes results in the production library running out of room, even though the repository showed plenty of nominal space. Adding tapes in this case results in even smaller tapes as well.
•Collocation of backups with many partial tapes might make the repository appear to have much space, but the partial tapes use more space than expected because of the size and usage. In this case, limiting the tapes to a smaller size could enable the tapes to store data more efficiently.
•Finally, if the repository has more space available when you multiply the total number of tapes by the amount of space, then it is a good plan to add more limited cartridges (This situation will not happen if you do not have any limited size tapes.)
If you have a mixture of tape sizes and types, the management of these tapes becomes complicated, especially if you have a large variance in the sizes. If you want to “unlimit” all of your existing tapes, contact IBM Support and request help with running the support utility to “unlimit” the cartridge sizes.
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