How to Handle Data Loss and Backup - High-Performance Web Databases: Design, Development, and Deployment - page 715

Using a typical tape rotation schedule results in a reasonable backup, as
long as the tape containing the backup is moved to a secure off-site loca-
tion. Unfortunately, most backup tapes never make their final journey. Left
unprotected in the same area where servers are, they are subject to the
same event that might cause the primary data source to be lost. A vigorous
off-site storage transfer and management procedure is therefore necessary.

Employ a System That Can Be Connected to Multiple Disks

These disks must be adapted to provide limited random access. Organi-
zations using this arrangement must have sophisticated on-site manage-
ment, and even with it, they face many of the problems common to tape
systems. This arrangement also does not aid in disaster recovery.

When data is written to disks simultaneously over the same channel, a
fault-tolerant mechanism protects the information. Although this approach
is better than nothing, a failure encompassing more than just the storage
device would render both sources of data unavailable. Adding channel
extension and disk duplexing to this arrangement provides added redun-
dancy. However, if both disks are in the same server, a single event could
still compromise both sources of data.

Another option may be the use of a Redundant Arrays of Inexpensive
Disks (redundant array of inexpensive disks). Spreading data across multi-
ple drives obviously reduces the risk associated with the failure of a single
drive. However, the use of Redundant Arrays of Inexpensive Disks does not
eliminate the need to backup.

Use an Off-Site, Electronic Vaulting Service

Using these services eliminates the maintenance and recovery problems
associated with backing up data files. Although this type of service has
been available for many years for mainframes, it is just becoming available
for local area networks and microcomputers. For example, Surefind, using
technology developed by AT&T Commvault Systems, can back up UNIX,
Digital Equipment Corporation-VMS, Novell Netware, and MS-DOS and can
transmit data over ordinary telephone lines to a secure location containing
optical storage devices.

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These services usually incorporate optical media with either Write-Once
Read Many (WORM) or erasable optical disks. Because the optical disk is a
random-access unit (as opposed to sequential tape), lost files are available
directly, and because the storage mechanism is located at a distance from
the primary place where data is stored, this type of service offers real data
processing disaster recovery capabilities. Outsourcing the backup mecha-
nism to a third-party source may therefore be the most reasonable solution
for the small and medium user.