I don't think a tape silo is the same thing. These were often used in universitiies to store the equivalent of a users "my documents"on, and whe some one logged on their data was copied down from the cylinder onto a track on disk. Try doing that with DLT, its trylely linear in access.
Modern SAN can have storage level migration though, so SSD disks doe really fas files, slower files on SAS (Serial Attached SCSI) and the real slow stuff on SATA disk.
Again data can be migrated to faster storage when needed....