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## Synchronous mode copy considerations 

Synchronous mode copy waits for the completion of remote write operation when explicit or implicit synchronous CCW is issued by mainframe or TS7700 internal buffer becomes full. For a single application perspective, the elapsed time might become longer than other copy modes when network latency is relatively long. For example, the required time for DFSMShsm secondary space management might be affected in the longer network latency. 

## 12.7.4 Tuning possibilities for copies: COPYCOUNT Control 

Tuning the counts of the number of concurrent copy jobs over the grid links can be done for several reasons, 

Values can be set for the number of concurrent RUN copy threads and the number of Deferred copy threads. The allowed values for the copy thread count are 5 - 128. The default value is 20 for clusters with two 1-Gbps Ethernet links, and 40 for clusters with four 1-Gbps or two 10-Gbps Ethernet links. Use the following parameters with the LIBRARY  command: 

GLYPH<SM590000> SETTING, COPYCNT, RUN 

GLYPH<SM590000> SETTING, COPYCNT, DEF 

## Increase the copy count 

Increasing the copy count can be beneficial if the following conditions exist: 

GLYPH<SM590000> The gridlinks are not saturated. 

GLYPH<SM590000> The number of small logical volumes is high. 

GLYPH<SM590000> An upgrade from 2 to 4 grid links was made, and the number of copy tasks were not adjusted. 

In this case, an increase of the copy count might reduce the RPO. 

Be aware that often one gridlink with 1 Gbps can be saturated by 10 copies running in parallel. If the logical volumes are small, you might see gaps in the grid link usage, when only a few copies are running, because some volumes finished, and new lvols where selected for copy processing. In this situation, it might be beneficial to have more copies running concurrently. 

Consider that if too many copies are running concurrently, the grid link is overflowed. This issue can result in package loss and retries, and lead overall to a lower performance of the grid link environment. 

If you want to increase the number, do so in smaller steps (5 or 10) to become familiar with the new setting. In addition, do not define values that are too high, especially if you use synchronous mode copy concurrently to the RUN and Deferred traffic. 

