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The circle on the graph that is shown in Figure 12-8 shows this algorithm in effect. During the 16:15 to 16:45 intervals, the amount of premigrate activity is limited. During the next six intervals, the premigration activity is zero. After this period of intense host activity and CPU usage, the premigrate tasks are allowed to start again. 

## 12.6.2 Premigration and premigration throttling values 

<img src='content_image/972857.jpg'>

The premigration and premigration throttling value parameters are used to define actions, which are triggered by the amount of non-premigrated data in the cache. Both values are applicable to the TS7700T only. 

## Premigration Priority threshold (PMPRIOR) 

When this threshold is crossed, premigration processes start and increase, and the host throughput tends to decrease from the peak I/O rate. The default value is 1600 GB. The TS7700T uses various criteria to manage the number of premigration tasks. The TS7700 looks at these criteria every 5 seconds to determine whether more premigration tasks must be added. Adding a premigration task is based on the following factors, among others: 

GLYPH<SM590000> Host-compressed write rate 

GLYPH<SM590000> CPU activity 

GLYPH<SM590000> Amount of data that must be premigrated per pool 

GLYPH<SM590000> Amount of data that must be premigrated in total 

## Premigration Throttling threshold (PMTHLVL) 

When this threshold is crossed, the host write throttle and copy throttle are started. The purpose is to slow incoming data to allow the amount of non-premigrated data to be reduced and not rise above this threshold. The default value is 2000 GB. 

The workload creating data (Host I/O, Copy, or remote write) in the TS7700T CP0 is not subject to throttling for these values. 

