Enterprises want “high availability” as part of data protection, yet virtually all use a “low availability” tape solution as part of their data protection strategy. For true data protection, enterprises should use multiple levels of availability in their overall strategies.
In an effort to ensure high availability for critical applications, many enterprises invest in additional, expensive disk storage arrays for an increased degree of physical availability. At the same time, they invest in tape automation solutions that add more levels of data protection, but that only deliver low availability (defined as hours or days to restore a particular pool of data).
In fact, enterprises can segment applications into ones that require high availability and ones that can function with low availability. Those applications, with their accompanying data that can get by with a tape automation solution alone, allow users to avoid the extra investment costs for additional disk storage. Note also that the most critical applications are (and should be) protected by both additional disk arrays and additional tape automation.
Thus, enterprises want and need multiple degrees of data protection. RAID on a production data array provides one degree of physical protection (as the failure of one disk drive can be tolerated without loss of data).
A remote mirror can provide a second degree of protection. Where information cannot be lost, a tape solution provides a minimum of one (and generally more, through multiple-generation tape copies) additional degree of protection.
Disk does not provide logical data protection; tape does (since the tape is outside the I/O “write” stream that can make logical changes to data).
Point-in-time copy capability and its derivatives can provide logical data protection on disk, but require understanding, planning, and investment that many IT organizations have yet to make.