Dynamic management of expandable cache storage for multiple network shares configured in a file server

Expandable cache management dynamically manages cache storage for multiple network shares configured in a file server. Once a file is written to a directory or folder on a specially designated network share, such as one that is configured for "infinite backup," an intermediary pre-backup copy of the file is created in an expandable cache in the file server that hosts the network share. On write operations, cache storage space can be dynamically expanded or freed up by pruning previously backed up data. This advantageously creates flexible storage caches in the file server for each network share, each cache managed independently of other like caches for other network shares on the same file server. On read operations, intermediary file storage in the expandable cache gives client computing devices speedy access to data targeted for backup, which is generally quicker than restoring files from backed up secondary copies.