Glossary

From Sysadmin

An internet

Any network of computers comprising multiple subnets that communicate using the TCP/IP protocol suite that are seperate from The Internet.

World Wide Web

The set of web sites accessible by web browsers using the HTTP protocol and related protocols.

Backup policy

an organisation's procedures and rules for ensuring that adequate amounts and types of backups are made, including suitably frequent testing of the process for restoring the original production system from the backup copies.

Backup rotation scheme

a method for effectively backing up data where multiple media are systematically moved from storage to usage in the backup process and back to storage. There are several different schemes. Each takes a different approach to balance the need for a long retention period with frequently backing up changes. Some schemes are more complicated than others.

Backup site

a place where business can continue after a data loss event. Such a site may have ready access to the backups or possibly even a continuously updated mirror.

Backup software

Software applications that are used for performing the backing up of data, i.e., the systematic generation of backup copies.

Backup window

the period of time that a system is available to perform a backup procedure. Backup procedures can have detrimental effects to system and network performance, sometimes requiring the primary use of the system to be suspended. These effects can be mitigated by arranging a backup window with the users or owners of the system(s).

Cold standby

Data recovery

the process of recovering data from storage devices when the normal operational methods are impossible. This process is typically performed by specialists in controlled environments with special tools. For example, a crashed hard disk may still have data on it even though it doesn't work properly. A data salvage specialist might be able to recover much of the original data by opening it up in a clean room and tinkering with the internal parts.

Deduplication

The act of removing or linking duplicate copies of data. In many filesystems duplicate copies can be [hard linked]] together so that only one copy is stored on the filesystem but appears to be multiple locations.

Differential backup 

a cumulative backup of all changes made since the last full backup. The advantage to this is the quicker recovery time, requiring only a full backup and the latest differential backup to restore the system. The disadvantage is that for each day elapsed since the last full backup, more data needs to be backed up, especially if a majority of the data has been changed.

Disaster recovery

the process of recovering after a business disaster and restoring or recreating data. One of the main purposes of creating backups is to facilitate a successful disaster recovery. For maximum effectiveness, this process should be planned in advance audited.

Disk image

a method of backing up a whole disk or filesystem in a single image. Since the underlying data structures are what is actually backed up, this method does not allow for file level control over what is selected for backup or restore.

Fire fighting

A colloquial term used among sysadmins (and others like engineers) to refer to reactive work such as fixing operational problems. Fire fighting is undesirable and a key aim of system administration is to build systems that develop as few operational problems as possible, or if they do that they can self-heal.

Full backup 

a backup of all (selected) files on the system. In contrast to a drive image, this does not included the file allocation tables, partition structure and boot sectors.

Hot backup

a backup of a database that is still running, and so changes may be made to the data while it is being backed up. Some database engines keep a record of all entries changed, including the complete new value. This can be used to resolve changes made during the backup.

Hot standby

Incremental backup

a backup that only contains the files that have changed since the most recent backup (either full or incremental). The advantage of this is quicker backup times, as only changed files need to be saved. The disadvantage is longer recovery times, as the latest full backup, and all incremental backups up to the date of data loss need to be restored.

Media spanning 

sometimes a backup job is larger than a single destination storage medium. In this case, the job must be broken up into fragments that can be distributed across multiple storage media.

Nibble 

Restore time 

the amount of time required to bring a desired data set back from the backup media.

Retention time 

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.

Staging area

Online storage used to store a copy of a backup before it is transferred to the backup device. Coping data to a staging area may be faster and more reliable than copung it directly to the backup device. Deduplication can be performed in the staging area.

System administration 

System administration is those tasks necessary for the functioning of a computer system or network that cannot be performed by the systems and networks themselves.

Tape library

a storage device which contains tape drives, slots to hold tape cartridges, a barcode reader to identify tape cartridges and an automated method for physically moving tapes within the device. These devices can store immense amounts of data.

The Internet

A global network of computers that communicate using the TCP/IP protocol suite.

Virtual Tape Library (VTL) 

a storage device that appears to be a tape library to backup software, but actually stores data by some other means. A VTL can be configured as a temporary storage location before data is actually sent to real tapes or it can be the final storage location itself.

Warm standby