Your backup glossary

While the perils of not having a proper backup solution are widely known (you'll lose a lot of time and money if you suddenly can't get at your application or files, basically), not everyone out there is clear on how to start implementing a plan, or what kind of backup strategy they need.

Even if you know your options, choosing between options can be a challenge - especially if you don't speak the lingo. Backup and archive is as full of acronyms, abbreviations and just plain odd terms as every other area of IT, and it can make working out what you actually need a bit of a minefield. With that in mind, we asked our consultants to define some of the most common buzzwords, just to help you get started...

3-2-1 A popular backup strategy that suggests you have three copies of your data. Two copies should be onsite but on different devices in case one fails. One copy should also be kept offsite in case anything happens to your office. We recommend following this model.

Backup A copy of a file or application saved in case the original is lost. You can perform incremental backups or full backups of your systems and devices.

Backup rotation strategy Competing strategies that suggest how and when you should back up your data in order to maximise data retention but minimise the resources needed to maintain and implement backups. Common strategies include FIFO, GFS  and the Tower of Hanoi (all below).

Backup window The period of time in which it is most convenient for you to back up your data and applications. For example, if your business is open from nine to five Monday to Friday, your backup windows are from 5pm to 9am the next day, and all day over the weekend, as workers are not in the office so it doesn't matter if systems are slowed down by (or inaccessible because of) an ongoing backup, and there are no open files (many solutions do not back up open files). Knowing your backup window has a big impact on your choice of backup system, as different kinds are able to back up different volumes of data in given timeframes. If your setup is designed to perform an automated backup at a specific time, this is also sometimes referred to as a backup window.

Cloud backup Cloud backups are a form of offsite backup. Your backup is kept in cloud storage (hence the name). The cloud can be private (run on hardware that is reserved just for your company's use, regardless of where it's hosted or if you manage it yourselves) or public (in which you share storage with multiple other users, and it is managed by a third party). Factors to consider when choosing between the two include your budget, data security requirements and retrieval time targets.

Disk Usually, backing up to disk will refer to backing up to hard drives (HDDs) instead of tape storage. This has the advantage that it is generally faster to back up to and retrieve data from disks than it is tapes, but on the other hand the cost per TB is higher and they have a shorter shelf life.

FIFO First In, First Out or FIFO is a backup rotation strategy in which you constantly rewrite your newest files over your oldest and least useful files. For example, if you had seven disks or tapes and did one back up every day, every Monday you would write over the previous Monday's backup, lose the iterations of your work it contained and replace them with new ones. While this is simple and easy to organise, it does mean that if someone accidentally deletes a key file and doesn't notice until a week later, all the backups containing the file will have been overwritten.

Full backup A complete backup of all data on a machine or system, regardless of whether the data has changed since the last back up was performed. Usually performed a regular, fairly spread out intervals (e.g. weekly or monthly) and supplemented by incremental backups.

GFS (Grandfather - Father - Son) A tape rotation strategy that suggests you have three levels of backup, for example monthly (grandfather), weekly (father) and daily (son). To give an example, you might use drives 1-4 to back up Monday-Thursday. Friday's drive, 5, would be archived and replaced with a new drive, 6. The next week you would use 1-4 to back up Monday - Thursday, then archive 6 and replace it with 7. At the end of the month, you would archive the final Friday's tape. This system would mean that at any time, you would have access to a back up from every day in the last week, every Friday in the last month, and every month for however long you care to keep those backups for. Some systems also include an annual 'great grandfather' backup.

HDD A hard disk drive, sometimes called a hard disk. Common storage media.

Hosted backup A form of offsite backup in which your data is kept on storage that is hosted (i.e. housed and maintained) by a third party. For example, our Backup24 solution allows you to back up your files to a Tier 2+ UK datacentre which we maintain on our clients' behalf.

Incremental backup A backup which only copies files, applications or data which has changed since the previous backup. Quicker and easier than full backups, incremental backups are often performed hourly or daily in order to supplement full backups, which are carried out less frequently.

LTO Linear Tape Open is the standard format for magnetic tape storage. You'll hear tape storage referred to as 'LTO tapes' and tape libraries as 'LTO libraries' - all this means is that they are made up of tapes which use the LTO standard to store their data. The current version of the standard is LTO 7 (capacity: 6TB per tape). LTO 7 technology can write to LTO 7 or LTO 6 media, and read from LTO 7, LTO 6 and LTO 5 media.

Offsite backup A backup which is stored somewhere other than your primary location. These are useful in case your main office is affected by fire, flood or power failure, and are often an insurance requirement. Data can be copied to a drive or tape in your location and then removed (for example, if you were to save everything to a drive that was then couriered to a data centre), or transmitted to another location and backed up there. Cloud backups are a form of offsite backup.

Onsite backup A backup which is stored on your premises, rather than offsite. They are generally quicker and easier to retrieve from than offsite backups, so are useful if, for example, someone accidentally deletes something.

Snapshots A snapshot backup captures how the entire architecture of an application, device or system looks at a particular moment in time. Restoring a snapshot backup that was taken a week ago will restore the system to the settings, content, etc that was in place when the snapshot was taken; users will lose any content created since the snapshot, and any changes to their settings they've made in the past week will need to be made again. You can also mount your file system as it was at the time of the snapshot and retrieve individual files.

Tape Magnetic tapes have been a staple storage medium for donkey's years. Tape is ideal for backup and archive as it has a low cost-per-terabyte and a shelf life of up to 30 years (although it is generally slower to write to and retrieve from than disk storage). Tapes are written and read in a tape drive, and housed in tape libraries, sometimes referred to as LTO libraries after the standard used to store data on the tapes.

Tape library A piece of hardware designed to hold a large number of tapes, and which includes a robotic arm for reading and retrieving disks.

Tape rotation strategy Often used interchangeably with backup rotation strategy. Just means planning how to rotate your tapes so that you don't end up spending your entire budget filling your entire office with storage media.

Tower of Hanoi A backup rotation strategy based on the Tower of Hanoi puzzle. You take a series of tapes - let's say five, and let's say they're labelled A - E. Tape A is backed up every other day, B is backed up every fourth day, C every eighth day, and D and E are backed up on alternate 16th days. This gives you a range of restore options, while minimising the number of tapes needed.

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