How are images deleted from cache?

The timing for archiving studies is configured in Autopilot Management. Autopilot also controls study deletion from cache once the study has been archived. Autopilot deletes a study that has not yet been archived only if the Automatically Archive Incoming Studies checkbox in the Source Manager is cleared.

To manage the cache, Autopilot gathers statistics on the use of the cache, rather than straight percentages about the cache use, to effectively manage caches of different sizes.

To determine which studies are eligible for deletion and which studies should be archived first, Autopilot uses an algorithm that determines which studies have been least recently accessed. Studies that have been prefetched assume the access time and creation time attributes of the study they were prefetched for, so they are not deleted prematurely.

Study archiving usually occurs at night, when system activity is low—the default is between 20:00 and 6:00. However, study deletion can be set to occur any time during the day.

Threshold levels

Threshold levels set the aggressiveness of deletion activity. Autopilot monitors how full the cache is, and determines at which threshold level (amber or red) the image cache is at. The threshold indicates the number of hours left that the image cache is available for incoming studies. A web threshold can be set for the web cache when the Curator is used.

Level	How critical?
Amber	Non-critical need for additional image cache space Reflects the number of hours of image cache space needed to provide an alternate backup location if studies cannot be archived
Red	Critical; image cache is nearly full Additional space is urgently required
Web	Non-critical need for additional web cache space Applicable only when Curator is installed and configured Configured as the number of hours remaining before the web cache is filled, based on the current rate of wavelet compression images put there by the Curator

Understanding the relationship between Autopilot, archiving, locations, and cache type

Autopilot follows the rules configured in Autopilot Management. Autopilot can be configured to archive studies from an image cache to whatever libraries (archives) are configured, and Autopilot does not care what the archive media is. It also does not matter where the cache resides (that is, whether the image cache is on the Network Gateway or Archive Server); you set up Autopilot for each cache, whose details are already configured through Network Management and Cache Manager. Finally, no archiving takes place for images in the web cache; therefore, Autopilot removes studies from the web cache only when the web threshold is crossed.