Databases Reference
In-Depth Information
environment is defined as the database, connecting middleware, and appli-
cation front-end screens. These technologies are used to complement each
other to offer accuracy, reliability, and stability.
METHODS OF DATA PROTECTION
The common methods of data production include the following: (1)
tape; (2) mirroring (RAID 0); (3) data guarding (RAID 5); (4) duplexing; (5)
partitioning; (6) replication; and (7) clustering. Each of these are explained
further in this section.
Before investigating these different methods available for protecting a
database environment, this article discusses the business requirements for
data recoverability and availability. For example, if a database, in the event
of failure, would place individuals in a life-threatening situation or would
place the organization into financial chaos and eventual closure, then it is
necessary to implement all available methods to become 100% fault toler-
ant. However, if a failure would be merely an inconvenience, then a simple
tape backup procedure may suffice. Most organizations seek the middle
ground.
Tape Backup
Tape backup should form the foundation of a corporate backup strategy
because of its ease of use and low cost. In order for the tape backup mech-
anism to be useful it must be well designed and tested regularly. At a mini-
mum, backups should be performed on a daily basis and not less than
weekly. If possible, the entire database(s) should be backed up on a daily
basis. The database transaction logs should be backed up during and after
business hours, or whenever feasible to minimize the risk of lost data.
Mirroring
Mirroring or RAID 0 provides for duplicate sets of data on two separate
hard disk drives, a primary and a secondary. This is also known as a mas-
ter-slave configuration. For each logical write operation there are two
physical write operations to the hard disks. This scenario protects against
failure of an individual or set of drives. If either the primary or secondary
drive fails, the data on the surviving drive allows for system recovery. In
most situations, this option is ideal for protection of the database transac-
tion logs. However, it does not offer protection against multiple simulta-
neous failures.
Data Guarding
Data guarding or RAID 5 has the ability to stripe redundant data across
multiple drives (minimum three) in an array. The striping of data protects
against a single drive failure in the array. When an array loses a drive, the
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