SAM extends the QFS file system transparently to archival storage. A SAM-QFS file system may have a relatively small (gigabytes to terabytes) "disk cache" backed by petabytes of tape or other bulk storage. Files are copied to archival storage in the background, and transparently retrieved to disk when accessed. SAM-QFS supports up to four archival copies, each of which can be on disk, tape, optical media, or may be stored at a remote site also running SAM-QFS.
Shared QFS adds a multi-writer global filesystem, allowing multiple machines to read from & write to the same disks concurrently through the use of multi-ported disks or a storage area network. (QFS also has a single-writer/multi-reader mode which can be used to share disks between hosts without the need for a network connection)