For most organizations, loss of data and offline time are not acceptable. Database backups are essential to ensuring data availability. When data availability is critical, a standby-by copy of the primary database will be maintained. Applications can read from either at any time provided the backup is updated synchronously (called a "hot standby"). A **full backup** is when the entire database is copied. An **incremental backup** will copy only changes made since the last backup. A **cold backup** is when the primary database is shut down for the time its being backed up. A **warm backup** does not require downtime, however it is slower. In many cases, transaction logs are used to replicate transactions that occur on the primary database to the secondary database. This is called **replication**. **Synchronous replication** applies transactions from the logs one at a time and are typically safer. **Asynchronous replication** applies transactions in parallel, which is faster but may result in inconsistent data. During a backup, the transaction logs are also backed up. To recover a database, find the most recent backup and apply any transactions not yet applied to the backup since the last backup.