Environment : All versions of Airwave
It's important to set Client Data Retention Interval to something low after a new install to a value between 14 to 31 days. This value should be as low as possible for the Public wi-fi deployments that have a lot of unique users.
When Airwave sees a first user, it creates an RRD file to store user's details like bandwidth, signal, goodput, health etc. The setting in the Client Data Retention interval determines how big the file should be. There is no way to shrink these files that have been created. Hence a higher setting in a Public Facing Enterprise can easily occupy huge chunks of disk space.
RRD files are used for storing data that's displayed in the time-sequence graphs (ie client count over the last year, bandwidth used over the last month).
Also, it's important to note that this setting only affects time-based graphs on user-specific pages. It doesn't impact the historical client data that is used for reports, it doesn't affect the storage of historical session details, and it doesn't affect data at the AP, folder or group level.
Hence this setting should be set to something low.