Archive and Backup.
High media capacity
High-performance read/write streaming
Low storage cost per GB
Performance is an important factor for backup, but since most backup operations involve large data sets, the ability to quickly stream information to and from the backup media is a first priority. Fast random access to small data sets during restore operations is typically less important. As an insurance policy, it is also necessary to minimize backup expense by reducing the cost of each stored record. The media of choice for backup and disaster recovery applications has traditionally been magnetic tape since it satisfies the performance and cost criteria of most organizations.
Extended media longevity
High-performance random read access
Low total cost of ownership
Archival storage requirements are quite different from those of backup operations. Media longevity and data authenticity feature much more prominently in archive environments. The storage media used within an archive should have a stable, long life to avoid frequent data migration over decades of storage. In order to comply with corporate and government regulations on data authenticity, it is crucial that information be protected from modification.
Time Machine is a backup system that will, once the capacity of the drive has been reached, delete old files in order to continue to backup.
This deletion process means that Time Machine cannot be classed as an Archival system.
Remember too that Time Machine is running on a Hard Drive which, as we all know, is going to fail at some point. Once it fails, the data are gone.