If your disaster recovery system is not in constant standby mode, for example if it is being used for another less important system, it will need the relevant software installed. All of this software is probably available from backups. Even so, copies of the software should be available locally, ready to install just in case. However, that this may require upgrading of the operating system, if the system is not on the same release. Where possible, on the disaster system, one should go for a combination of versions and releases that has been tested in normal running.