The basic concept of a disaster recovery site is that it can provide a base from which the company can be operated during a disaster. The disaster recovery site is not normally intended to provide a desk for every employee, but is intended more as a means to allow key personnel to continue the core business function.
In general, a cold recovery site is a site that can be up and operational in a relatively short time span, such as a day or two. Provision of services, such as telephone lines and power, is taken care of, and the basic office furniture might be in place, but there is unlikely to be any computer equipment, even though the building might well have a network infrastructure and a room ready to act as a server room. In most cases, cold sites provide the physical location and basic services.
Cold sites are useful if there is some forewarning of a potential problem. Generally speaking, cold sites are used by organizations that can weather the storm for a day or two before they get back up and running. If you are the regional office of a major company, it might be possible to have one of the other divisions take care of business until you are ready to go; but if you are the one and only office in the company, you might need something a little hotter.
For organizations with the dollars and the desire, hot recovery sites represent the ultimate in fault-tolerance strategies. Like cold recovery sites, hot sites are designed to provide only enough facilities to continue the core business function, but hot recovery sites are set up to be ready to go at a moment's notice.
A hot recovery site will include phone systems with the phone lines already connected. Data networks will also be in place, with any necessary routers and switches plugged in and turned on. Desks will have desktop PCs installed and waiting, and server areas will be replete with the necessary hardware to support business-critical functions. In other words, within a few hours, the hot site can become a fully functioning element of an organization.
The issue that confronts potential hot-recovery site users is simply that of cost. Office space is expensive at the best of times, but having space sitting idle 99.9 percent of the time can seem like a tremendously poor use of money. A very popular strategy to get around this problem is to use space provided in a disaster recovery facility, which is basically a building, maintained by a third-party company, in which various businesses rent space. Space is apportioned, usually, on how much each company pays.
Sitting in between the hot and cold recovery sites is the warm site. A warm site will typically have computers but not configured ready to go. This means that data might need to be upgraded or other manual interventions might need to be performed before the network is again operational. The time it takes to get a warm site operational lands right in the middle of the other two options, as does the cost.