Availability - Fall-back, hot site, warm site

Fall-back is the manual switch-over to a identical standby computer system in a different location.

There are three basic forms of fall-back services, with some variations:

  • Hot site
  • Warm site
  • Cold site

Hot site

A hot site is a fully configured computer facility with electrical power, heating, ventilation, and air conditioning (HVAC), and functioning file/print servers and workstations. The applications that are needed to sustain remote transaction processing are installed on the servers and workstations and are kept up-to-date to mirror the production system.

Theoretically, personnel and/or operators should be able to walk in and, with a data restoration of modified files from the last backup, begin full operations in a very short time.

If the site participates in remote journaling, that is, mirroring transaction processing with a high-speed data line to the hot site, even the backup time may be reduced or eliminated.

This type of site requires constant maintenance of the hardware, software, data, and applications to be sure the site accurately mirrors the state of the production site. This adds administrative overhead and can be a strain on resources, especially if a dedicated disaster recovery maintenance team does not exist.

Warm site

A warm site could best be described as a cross between a hot site and cold site. Like a hot site, the warm site is a computer facility readily available with electrical power and HVAC and computers, but the applications may not be installed or configured.

It may have file/print servers, but not a full complement of workstations. External communication links and other data elements that commonly take a long time to order and install will be present, however. To enable remote processing at this type of site, workstations will have to be delivered quickly and applications and their data will need to be restored from backup media.

Cold site

A cold site differs from the other two in that it is ready for equipment to be brought in during an emergency, but no computer hardware (servers or workstations) resides at the site.

The cold site is a room with electrical power and HVAC, but computers must be brought on-site if needed, and communications links may be ready or not. File and print servers have to be brought in, as well as all workstations, and applications will need to be installed and current data restored from backups.

If an organization has very little budget for an alternative backup processing site, the cold site may be better than nothing.

Service Bureaus

In rare cases, an organization may contract with a service bureau to fully provide all alternate backup processing services. The big advantage to this type of arrangement is the quick response and availability of the service bureau, testing is possible, and the service bureau may be available for more than backup.

The disadvantages of this type of setup are primarily the expense and resource contention during a large emergency.

This entry was posted on Wednesday 27 July 2011

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Sjaak Laan

Recommended links

Ruth Malan
Gaudi site
Esther Barthel's site on virtualization
Eltjo Poort's site on architecture


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