The dmdaemon uses the key to look-up the file info in the DMF database. The MSP is contacted to bring the data blocks back online. Once back, and attached to the inode, the sleeping process is waked and scheduled to run just as if the file had resided on disk all along. Only regular files may be migrated, directories, soft links, pipes, device nodes, etc cannot. Offline files have no data blocks on the disk.
Dual file have their data blocks copies to off-line storage but also have the blocks online.
If file system space is getting tight, dual state files are targeted since the blocks are already off-line the online blocks are simply removed. An MSP is an agent that moves the data blocks to off-line storage. The tape MSP is used if your system has directly attached tape drives and tape vault. The ftp MSP is used to move the disk blocks to another computer system via the ftp utility. If HPSS is down, the ftp agent will fail to connect and re-try again in 5 minutes.