With the release of V7.20, a feature called persistence can be applied to I/O devices. When implemented, the tag cache for an I/O device is written to an XML file at a set period, allowing the last available data to be reloaded following a shutdown. Persistence is enabled using the Persist field in the extended section of the I/O Devices Properties dialog.
A persisted memory I/O device is recommended as an improved alternative to a disk I/O device, as synchronization is supported if a server becomes unavailable for a period of time.
Note: It is recommended that data assigned to disk I/O devices be migrated to the new persisted memory I/0 mode. See the topic Persisted I/O Memory Mode for information on how to migrate a disk I/O device to a persisted memory I/O device.