Page348

Differential Backups

Differential backups operate in a similar manner as the incremental backups except for one key difference. Differential backups archive data that have changed since the last full backup.

For example, the same site in our previous example switches to differential backups. They lose data after the Wednesday differential backup. Now only two tapes are required for restoration: the Sunday full backup and the Wednesday differential backup.

Tape Rotation Methods

A common tape rotation method is called FIFO (First In First Out). Assume you are performing full daily backups, and have 14 rewritable tapes in total. FIFO (also called round robin) means you will use each tape in order, and cycle back to the first tape after the 14th is used. This ensures 14 days of data is archived. The downside of this plan is you only maintain 14 days of data: this schedule is not helpful if you seek to restore a file that was accidentally deleted 3 weeks ago.

Grandfather-Father-Son (GFS) addresses this problem. There are 3 sets of tapes: 7 daily tapes (the son), 4 weekly tapes (the father), and 12 monthly tapes (the grandfather). Once per week a son tape graduates to father. Once every 5 weeks a father tape graduates to grandfather. After running for a year this method ensures there are backup tapes available for the past 7 days, weekly tapes for the past 4 weeks, and monthly tapes for the past 12 months.

Electronic Vaulting

Electronic vaulting is the batch process of electronically transmitting data that is to be backed up on a routine, regularly scheduled time interval. It is used to transfer bulk information to an offsite facility. There are a number of commercially available tools and services that can perform electronic vaulting for an organization. Electronic Vaulting is a good tool for data that need to be backed up on a daily or possibly even hourly rate. It solves two problems at the same time. It stores sensitive data offsite and it can perform the backup at very short intervals to ensure that the most recent data is backed up.

Because electronic vaulting occurs across the Internet in most cases, it is important that the information sent for backup be sent via a secure communication channel and protected through a strong encryption protocol.

Remote Journaling

A database journal contains a log of all database transactions. Journals may be used to recover from a database failure. Assume a database checkpoint (snapshot) is saved every hour. If the database loses integrity 20 minutes after a checkpoint, it may be recovered by reverting to the checkpoint, and then applying all subsequent transactions described by the database journal.

Remote Journaling saves the database checkpoints and database journal to a remote site. In the event of failure at the primary site, the database may be recovered.

Database Shadowing

Database shadowing uses two or more identical databases that are updated simultaneously. The shadow database(s) can exist locally, but it is best practice to host one shadow database offsite. The goal of database shadowing is to greatly reduce the recovery time for a database implementation. Database shadowing allows faster recovery when compared with remote journaling.