Data Center Affinity is a feature in GTM which helps you to control end user's movement different more than 2 data center. GTM does a great job by mapping an end user to a DC to which it hast the best connectivity. However, if a user is roughly equidistant from two data centers causing similar, their ping score will be similar for both DC.In this case, the user's may switch back and forth between 2 Datacenter due to minor variation in ping scores.
Data Center Affinity allows to control this behavior. Data Center Affinity tell GTM not to reassign a user to different data center until and unless performance has improved to configured threshold value. Correctly configured, this keeps small variations in ping scores from flipping users from data center to data center, but allows users to be moved when the score difference is so great that their performance would suffer otherwise.
Data center affinity is controlled by two parameters.
1. Threshold percent
2. Threshold constant.
The threshold percent is a percentage of the score for a data center; the threshold constant is an absolute number. Data center scores are measured in milliseconds (corresponding to ping round-trip times); geographic distances are converted to an equivalent ping time. If you configure a threshold percent of 10 percent, then a user will not be reassigned to a data center with a better score unless the score is more than 10 percent better than the score for the current data center. Similarly, if you configure a threshold constant of 100, then an end user will not be reassigned to a data center with a better score unless the score is more than 100 milliseconds better than the score for the current data center.