A method and apparatus for storing on centralized mass storage devices archival data from multiple computers in a networked environment. In a networked computer system having a communication network interconnecting one or more computers and a storage unit, parallel processes are created to perform repeated backup operations for disks on computer devices on the communication network. The backup operations for a disk include a backup initialization which occurs when a primary storage device does not have a full index or a backup data file for a disk but a secondary storage device does. During a backup initialization, data from the files and directories on that disk along with an index entry for each file or directory are passed to the primary storage device which directly passes that information directly through to the secondary storage device. The index entries are incorporated into a full index and the data is incorporated into a backup data file. During a backup cycle, the computer device is incrementally backed up to a primary storage device such that the primary storage device contains a full index with an entry for each file and directory on the disk and a backup data file for the disk with data for the files and directories which have been changed or created since the last backup to the secondary storage device occurred. When a specified, predetermined time or event occurs or the transfer is otherwise indicated, the primary storage device transfers the full index and the backup data file to the secondary storage device.