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This is part seven of the series that began with
What is System Managed Storage?
What is tape mount management?
Tape mount management (TMM) is a methodology for providing efficient use of tape media and reducing the costs associated with tape data sets without requiring you to make JCL changes. This methodology can help because:
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Often a tape is mounted to write a single data set. The progression from 3420 to 3480 to 3490E to 3590 represents a
24,000% increase in volume capacity, while 70% of tape data sets continue to be less than 10MB in size. This represents substantial wasted tape capacity.
Using TMM, you can reroute such allocations to DASD, eliminating costs associated with the tape mount and improving job performance. There is no wait for a tape mount and I/O can be performed at DASD or cache speed.
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Once you have rerouted allocations to DASD, you can use DFSMShsm to migrate data sets. This reduces the number of tape mounts as it allows multiple data sets to be written to a single tape.
Most installations can easily reduce mounts between 30% to 50%. This usually reduces the tape cartridge inventory accordingly. It also frees up 25% to 33% of the tape drives because jobs are no longer queued on them.
- Because DFSMShsm can pack multiple data sets on a single tape, it make more efficient use of tape media and may allow you to reduce your tape inventory. DFSMShsm fills
all volumes to 94% regardless of capacity.
How do I implement tape mount management?
Implementing the tape mount management methodology involves the following steps:
- Analyze tape usage
The volume mount analyzer is a tool that can help you analyze your current tape environment. It produces reports that profile your tape mount workload and tape media usage, so that you can decide whether tape mount management might benefit your installation.
The volume mount analyzer uses your installation's SMF data to analyze tape mount activity and to produce reports that help you:
- Identify trends in tape mounts, data set names, jobs, programs, and data set size
- Evaluate the tape hardware configuration
- Quantify the benefits of tape mount management
- Determine which data sets are good candidates for tape mount management.
- Determine data class and management class requirements for candidate data sets
- Develop ACS routines to select candidates and exclude data sets that must remain on tape
- Determine the size of the DASD buffer and high and low thresholds needed for the buffer's storage group.
- Set aside a DASD buffer for tape data sets
Because tape mount management causes data sets to be redirected from tape to DASD, you will need some additional DASD space. The volume mount analyzer can help you determine how many volumes you will need.
IBM recommends that you dedicate specific volumes in a special TMM storage group, since the management requirements for this storage group tend to be different from other storage groups. For example, the TMM storage group may fill up several times a day, requiring that interval migration be used to ensure that sufficient space is available for new allocations. However, you may choose not to use interval migration in your other storage groups.
- Define SMS constructs for tape mount management
After you identify the data sets to be redirected from tape to DASD, you need determine management class attributes for them. You should consider residency time on primary and migration level 1 (ML1) storage, as well as the amount of space required to store the data set versus the number of mounts required to recall the data. The volume mount analyzer produces reports to help you determine the requirements for your TMM management classes.
You also need to define data classes for TMM. Most tape allocations do not specify space. Redirecting these allocations without providing space parameters results in allocation failures. You can use data classes to prevent such failures. The volume mount analyzer will assist you in determining the space values.
You will probably also want to create a TMM storage class. Assigning this storage class to the data sets makes them SMS-managed. It also allows you to identify redirected data sets in the storage group ACS routine and direct them to the TMM buffer.
- Write ACS routines to redirect tape allocations to DASD
Using information provided by the volume mount analyzer, you can develop filters to ensure that only those data sets you want redirected from tape to DASD are assigned SMS classes and groups. By using the ACS routines to do this, you can take advantage of TMM without changing any JCL. The ACS routines automatically assign classes and groups to the data sets, and the system then directs the data sets to the TMM buffer.
- Use DFSMShsm to migrate data sets directly to tape as a group
DFSMShsm can automatically migrate the data sets you redirected to tape. You will probably want to use interval migration in your TMM buffer pool to ensure that data sets are periodically moved from DASD to tape to make space for more data sets. This approach works well with these data sets, because many of them are written and then never re-read.
How can I be sure TMM is helping me?
The volume mount analyzer allows you to run a top report (of your major tape users) and an estimate report. Using the estimate report, you can quantify the cost of your DASD buffer as contrasted with the savings you get by redirecting allocations from tape to DASD.
In summary
You can use the tape mount management methodology to improve efficiency of tape usage and reduce the costs associated with tape data sets without having to change JCL.
- Over 2500 IBM customers are now doing some form of TMM
- There are documented cases in which using TMM has eliminated the need for 90 automated tape libraries, 47 tape operators, and several hours of batch window
- One very large customer who implemented TMM now has an average utilization of 70% on
all 300,000 3490E tape cartridges
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