Glossary
Warm site
A warm site is a standby facility with hardware installed and copies of production data available, but no live workloads running. It recovers in hours to days, slower than a hot site and much faster than a cold site, because equipment is already in place and only data and services need bringing up.
How data reaches the site
Two warm sites with identical hardware can have very different recovery numbers, because the difference lies in how the data gets there.
| Data path | Typical data loss | Typical time to recover | Bandwidth and cost |
|---|---|---|---|
| Backups restored on a schedule | Up to about a day | One to three days | Low |
| Continuous replication | Seconds to minutes | Hours | Higher |
What takes the time at takeover
The team brings data to the latest available point, starts databases and then the applications that depend on them, and redirects users through DNS or load balancers. Procurement, the step that dominates a cold site, is already done. What remains is work: applying the last changes, starting systems in order and checking they behave.
Standby drift
A site that nobody uses falls behind production. Patches, certificates, firmware and firewall rules reach it late or never, and at takeover an application fails to start on a stale library. Sites that are patched and test-started on a schedule avoid most of this. Some organizations run development or test work on the hardware between events, which keeps it exercised and is cleared on takeover. Systems that cannot wait hours belong on a hot site, and a business impact analysis shows which ones those are.
Warm sites built on rented capacity
A warm site no longer has to be a second building. Some organizations keep data copies in a provider's storage and start compute there only when needed, so they pay for storage continuously and for servers only during a test or a takeover. The trade is control over capacity: in a regional event, many customers may try to start servers in the same place at the same time, and the recovery time depends on that capacity being available.