Reading 3: Backup Availability

Reading 3: Backup availability

An important aspect of the backup process is the accessibility of the data that has been backed up.

For example, if you are performing daily backups to tape and storing them offsite you are improving the protection of your backup but conversely you are slowing down the restoration process if data is lost. There is a constant balance that needs to be maintained between the security of backups and the time required to restore data.

The common availability models are: online, offline, near line, off site, data recovery centres and backup sites.

Online Online backup usually refers to backup storage that is immediately available. This typically refers to hard drives or drive arrays that are connected, powered and visible to the backup software for restoration.

This has the advantage of allowing very rapid recovery of data. For example, a manager has to give a presentation in an hour but has accidentally deleted the presentation file. Online backup would allow the immediate recovery of the lost file to the time of the previous backup.

The most significant disadvantage is that the backup is typically stored in close proximity to the data source for the backup. Therefore, in a significant disaster such as a fire, flood or earthquake, the chances of loosing the original data and the backup are high.

Offline Offline backup is the opposite of online backup. The storage medium used for the backup is not connected and instantly accessible. In offline backup a person must be present to obtain the storage medium and make is visible to the backup software. This usually

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involves inserting the medium into a drive or port, such as inserting a tape into a tape drive. Typically, the storage mediums used include magnetic tape, CD (CD-R, CD-RW), DVD (DVD-RAM, DVD+-R, DVD+-RW, dual layer DVD), flash based drives (USB drive), and disks (3.5 inch diskette, ZIP disks).

These forms of media are cheap and portable, allowing for easy offsite storage. The most significant disadvantage is that human intervention is required to access the media. If data is lost outside of normal working hours it could take some time for an IT staff member to get on-site to make the media available to the backup software.

Near line Near line backup storage is a compromise between online and offline backup. Typically the storage media of offline backup is used, such as magnetic tape, but no human intervention is required to make the tape available to the backup software. This is usually achieved through an auto-loading (robotic) tape system. In high end robotic systems, a tape library can consist of hundreds of tapes, multiple tape drives and a robotic loading system.

Near line systems have the advantage of using cheap media which can be taken off site for safe storage and, auto-loading systems do not require a human to be present. However, near line systems are still slower than online systems and auto-loading hardware is expensive.

As hard drive capacities continue to increase and their cost drops, the advantages of offline and near line systems are diminishing. For small to medium size companies the use of portable hard drive backup systems capable of storing up to a terabyte of data are becoming very cost effective.

Off site Off site backup refers to storing backup media at an alternate location. This may be as simple as a member of the IT staff taking monthly tapes home or as complex as backup data being sent to an alternate location within the same city, interstate and to international locations, often in secure environments.

Network based backup has allowed off site and online backup to converge. Backup data can be sent to a remote site via the Internet (or in highly mission critical systems via leased lines) to an online server. In the event of a disaster, data can be retrieved from the

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remote network store. Of course, this is dependant on whether network access is still available post disaster.

Data recovery centres In the event of a serious disaster where not only data is lost but the IT infrastructure is damaged (such as servers and networking devices), it may be necessary to have an alternate infrastructure available. This is usually only the case for businesses were system downtime will be very costly.

In most cases, a third-party provider is contracted to supply data recovery facilities where backups can be used to recreate core systems, allowing business functions to continue. In some cases companies may run their own data recovery centre.

Backup site Closely related to data recovery centres is the concept of a backup site. This is an alternate, remote site where resources, including staff, can be relocated to continue business operations. These sites are commonly graded as cold, warm and hot.

A cold site is merely an alternate physical premises and does not contain any data backups or hardware. This is the least expensive option but takes the most time to get a business back up and running.

A warm site is an alternate physical premises and includes the hardware required to operate the business. The hardware may be significantly less than at the working business site but needs to be adequate to run the core business operations. No backup data is stored at a warm site. This option is a good balance of cost and speed.

A hot site is an alternate physical premises containing all the required hardware and complete backups of data. The aim is to produce a mirror of the working business site to allow for rapid relocation and restoration of business functions. The disadvantage of such a site is the high cost.