Online Disk Snapshot

Some disk subsystems support taking a disk image snapshot without interfering with the running system. This option, when available, provides a way to backup TRNLOG files without losing data or producing an inconsistent transaction state. A disk snapshot does not include the contents of the server’s cache, so for non-transaction and PREIMG files updates may be lost. Non-transaction and PREIMG files restored from a disk snapshot should be re-created or rebuilt. For TRNLOG files, the transaction logs contain all committed updates, so the TRNLOG files can be restored to a consistent state by restoring the disk image and starting the c-tree Server, allowing it to perform automatic recovery on the TRNLOG files using the saved transaction logs.