As an optional feature, CA Disk can compress data as it is being written to the archive or backup data sets, whether they are on tape or disk.
If you activate data compression, the default technique is technique number 0. CA Disk-supplied technique number 0 typically reduces the space used by 40 to 50 percent, which yields the same reduction in the amount of tape used. However, if you archive to disk instead of tape, the disk savings achieved can be closer to three or four to one, or even much higher. This is due to the optimized storage techniques in the archives, as well as wasted space in the original data sets.
CA Disk users who are also licensed to use CA's CA Compress product, can specify technique number 1 to use CA Compress as the compression method. CA Disk supplies a formal interface to use this compression method. Instructions for implementation are listed in Using CA Compress within the Archives.
As a direct result of compression, the number of I/Os to the archive media is also reduced by the same percentage, which can provide a significant improvement if I/O contention is a problem in your installation.
To achieve these benefits, however, expect the CPU time to increase. For more information, see the section Data Compression Techniques in the chapter "Algorithms."
The following sysparms are used by data compression. See them for applicability in your installation:
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Sysparm |
Description |
|---|---|
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DCDATACP |
turns data compression off or on |
|
DCCOMPTC |
indicates the compression technique number |
|
DCCMPEXn |
exit for compression technique n |
|
DCDCPEXn |
exit for decompression technique n |
|
DCDSNDEX |
user exit for deciding if data compression is to be done for each data set, and what technique is to be used |
|
DCEXCTBL |
exclusion table name |
|
DCINCTBL |
inclusion table name (overrides DCDATACP"N") |
|
DCRTSTAT |
turns compression statistics off, on, or on with details for each data set compressed |
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