by April 3, 2003 0 comments



Most organizations have a haphazard backup plan or sometimes none at all. The companies risk losing critical data compiled over months, maybe years together. With an effectively planned backup strategy they’re not only insuring themselves against downtime and expense of lost data but also getting peace of mind in the bargain. Designing an effective backup routine involves three major steps:

Identify backup needs: Begin by assessing the amount of data and its criticality. Sort through the data to identify stuff that really needs backing up. User area and home directories on file servers usually hold documents, spreadsheets, and other files that are created and accessed daily. This volume should therefore be backed up daily. Applications and third-party software on the other hand is easier to re-install from scratch rather than restoring from the backup. Once you know the volume of data and its criticality, it’s easier to decide on the actual medium and the frequency of backups.

Snapshotting
In this age of 24/7 e-enabled businesses, management of data is very crucial to the success of any enterprise. Snapshotting of data is an important way that helps data administrators in large enterprises to keep business and IT processes rolling. A snapshot is a complete copy of the file-system (in one or more volumes/disks) at a certain point in time. These copies are taken on a periodic basis and stored safely on tapes or disks, onsite or offsite. Benefits of snapshotting include recovery of data in case of accidental deletions in a short time period, incremental back-ups and quick crash recovery, in case the main database is corrupted. Though snapshotting requires extra storage, overall, it takes only a fraction of the space that would be needed to back-up data using other methods. 

Devise a backup plan: Before a backup strategy is devised, a survey should be carried out to see what backup devices are available. Once this has been identified, an appropriate strategy can be devised. An important factor to consider is the human and material resources available to maintain the strategy.

Earlier a backup plan just involved copying files, but with time features such as tape tracking with write protection, cataloging and automation, and scheduling have become available. You also have to decide whether to go in for centralized storage or distributed storage. While a centralized storage strategy is easier to monitor, it has its own share of problems like increased traffic over the network. Moreover, distributed storage has become a reality with increased capacity of devices and the possibility of unattended backups. In general, centralized storage is preferred in large multi-server
organisations. 

Besides the transport logistics, you also have to devise a backup schedule. In general, a backup is classified as Incremental backup and Full System backup. Incremental backup only copies files that have changed or have been newly created since the last backup. It uses a file attribute called Archive Bit to mark files as having been backed up. When the file system modifies or creates a file, the archive bit is set, indicating that the file needs to be backed up. Backup software clears the bit when the file has been backed up. An incremental backup is less time consuming and usually used for daily backups.

Full System backups copy all server hard disk drives every day. While these are simple to administer and restore from, they’re very time consuming and therefore are usually done over the weekends when the network traffic is light.

Procure hardware/software: This is the final step in the building up of the backup strategy. The media and backup hardware you use depend on the volume and criticality of your data. A range of backup media is available, from low-cost 4 mm tapes and quarter-inch-cartridges to redundant hard disks. 

Various third-party software products are also very popular. In addition, major operating systems such as NetWare and Windows NT also have built-in utilities for automating backups.

Tape Rotation
Tape rotation refers to the reuse of tape media. You can reuse tapes on a rotating basis when the tapes are so far out of date that you no longer need the data. Some organizations may need to rotate only between two tapes while others will keep backups for up to a month. To implement a fail-safe plan, you must keep a recent full system copy off-site.

Single-tape cycle: This is the most basic type of backup regime you can have. It involves backing up data onto a single set of tapes and reusing the same tapes the next day. If you have a power failure at the time of backing up or if there’s some problem
with the tape drive, then you are left with no fallback.

Most organizations use one of the three tape rotation policies (see diagrams) for their backup.

PCQ Labs 

Six-Tape Cycle: 

Six-Tape Cycle:
You need a set of tapes for each weekday from Monday to Thursday plus two more. The four tapes are used for partial backups while the other two are used alternately for a full backup on each Friday. This way you can restore data up to
two weeks old. The regime can be extended to a month by using additional Friday tapes


Ten-Tape Cycle:
Also called the “Grandfather-Father-Son” model, this scheme uses ten units of backup media (where a unit can backup the entire system) to provide up to twelve weeks of coverage.

Label ten sets of media as: Monday, Tuesday, Wednesday, Thursday, Friday 1, Friday 2, Friday 3, Month 1, Month 2, and Month 3.

Start the cycle on a Friday and do a full backup on the Friday 1 tape. Every Monday to Thursday take incremental backups on the appropriately labeled tapes. Each Friday, use the next Friday media set to do a full backup. Every fourth Friday, use the month tape units to do a full backup. After four months, you start re-using the tapes


Three-Tape
Cycle:
This is another simple low-cost option. It involves using three sets of tapesfor taking backups. Upto three days old data can be restored

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