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Backup strategies
A backup should be planned carefully, and the following points should be considered:
- A backup should be easy to do.
- A backup should be automated and rely on as little human interaction as possible.
- Backups should be made regularly.
- Proper backup relies on at least two copies, stored on different media, kept at different locations.
- A backup should rely on standard, well-established formats.
- A backup should not use compression. Uncompressed data are easier to recover if the backup media are damaged or corrupted.
- A backup should be able to run without interrupting normal day-to-day work.
- If a backup spans multiple volumes, recovery should not rely on all volumes being readable or present.
- If you use a certain medium to do your backup on, you also need to have a drive available that can read it.
- Backup media need to be read from time to time, to make sure the data are still readable. Also, the data needs to be copied to a new (different) medium if it's about to disappear. Will you be able to read a CD-R in 10 years' time?
- Each of the different media have benefits and drawbacks. Also consider the cost per gigabyte when comparing different solutions.
Human factors to consider:
- In the case of a "disaster", no one will be able to think clearly, and act accordingly. For this reason, checklists need to exist that outline what to do (in what order).
- Staff needs proper training in what to do in case of such an "event" occurring.
Backup media types
As of 2005, backups are most often made from hard disk based production systems to large capacity magnetic tape, hard disk storage, or optical disk WORM media like CD-R, DVD-R and similar formats. As broadband access becomes more widespread, network and remote backup / online backups are gaining in popularity. There are quite a few companies offering Internet-based backup. During the period 1975-95, most personal/home computer users associated backup mostly with copying floppy disks. However, recent drop in hard disk prices, and its number one position as the most reliable re-write-able media, make it one of the most practical backup media.
A CD can be used as an alternative backup device. Great advantages of CDs are that they have a high-density storage media on a 4.75" reflective optical disc. They can hold up to 650 MB of data. This is equivalent to 12,000 images or 200,000 pages of text. CDs may all look the same, but there are many standards for different applications.
Special cases
Backing up active databases requires highly-specialized software that must be integrated with the database system in order to prevent data corruption. For example, a user accesses the website of his bank and transfers money from one of his accounts to another while a backup is running. Such a transaction will affect multiple places on the hard disks of the bank's systems.
At minimum, the amount of the transfer will be subtracted from the balance of one account, and added to the balance of the other account. If there is then a disk crash and restore, it is important to ensure that the database holding the user's account balances gets restored correctly. If the subtraction part is restored correctly but the addition part isn't, then the user is unhappy. If the addition part is restored correctly but the subtraction part isn't, then the bank is unhappy.
Metrics
There are six primary metrics relating to data backup:
- Recovery Point Objective (RPO) is the point in time that the restarted infrastructure will reflect. Essentially, this is the roll-back that will be experienced as a result of the recovery. Reducing RPO requires increasing synchronicity or frequency of copying the data to be protected.
- Backup Window is the amount of time that is taken to copy a given data set to the backup device. Most traditional backup systems require a data set to be frozen for hours while the entire content of a filesystem is copied to magnetic tape. Newer techniques use incremental backup forever as well as mirror, snapshot, effectively reducing the required backup window.
- Restore Time is the amount of time required to bring a desired data set back from the backup media.
- Retention Time is the amount of time in which a given set of data will remain available for restore. Some backup products rely on daily copies of data and measure retention in terms of days. Others retain a number of copies of data changes regardless of the amount of time.
- Backup Validation, also known as "Backup Success Validation", is the process by which Owners of data can get information regarding how their data was backed up. This same process is also used to prove compliance to regulatory bodies outside of the organization, for example, a biotech company might be required to show "proof" to the FDA that their test result data are backed up properly. Terrorism, data complexity, data value and increasing dependence upon ever-growing volumes of data all contribute to the anxiety around and dependence upon successful backups. For that reason, many organizations rely on third-party or "independent" solutions to test, validate, optimize and charge for their backup operations backup reporting modern backup to disk software have built-in validation capabilities.
- Open File Backup is the ability to backup a file while it is in use by another application.
Different roles of data backups
Computer backups are useful primarily for two purposes, the first and most obvious is to restore a computer to an operational state following a disaster also called disaster recovery. This includes loss of a hard disc or the file system becoming so badly corrupted it cannot be read. The second use, often overlooked but probably more common, is to facilitate the recovery of a single file or set of files when they are accidentally deleted or corrupted by the user or a program.
Backup procedures
Proper backup procedures require redundancy of the backup to a remote location and an effecitive Backup rotation scheme such as the GFS method (Grandfather-Father-Son Backup). Storing the copy near the original is unwise, since many disasters such as fire, flood and electrical surges are likely to cause damage to the backup at the same time.
The 2001 attacks on the World Trade Center presented many organizations with unprecedented disaster recovery scenarios, due to its scope. A few years earlier, during a fire at the headquarters of a major bank in Paris, system administrators ran into the burning building to rescue backup tapes because they didn't have offsite copies.
Recovery strategy
A backup is only as useful as its associated recovery strategy. Having a complete set of backup tapes is of no use if the only copy of the software required to read them is on one of the tapes. It is also possible for backup software to run successfully for several months, only to fail when it is needed most due to read errors on the backup media. Magnetic tapes in particular should be read-tested on a regular basis.---
Validation and Verification
Many backup programs make use of checksums or hashes. These offer several advantages. First, they allow data integrity to be verified without reference to the original file: if the file as stored on the backup medium has the same checksum as the saved value, then it is very probably correct. Second, some backup programs can use checksums to avoid making redundant copies of files, to improve backup speed. This is particularly useful when multiple workstations, which may contain duplicates of the same file, are backed up over a network: if the backup software detects several copies of a file having the same size, datestamp, and checksum, it can put one copy of the data onto a backup medium, along with metadata listing all places where copies of this file were found. Also, checksums can improve performance of the verification pass for backups across a network, by computing checksums independently on each computer, then sending only the checksum over the network so that checksums can be compared instead of actual data.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Backup".Zip Backup to CD
Zip Backup to CD is a data backup software designed to backup your data files to CD/DVD, using the standard Zip file format, allowing backup files to be viewed and restored with most zip file utilitie.... lęs mere 
