When creating a virtualization environment, it is crucial to ensure that your virtual machines will be protected in case of sudden failure. Snapshots record the data status of virtual machines and can be used to restore the virtual machines back to when the snapshot was taken. This article will explain the difference between the two types of snapshots in Virtual Machine Manager.

Crash-consistent snapshot

A crash-consistent snapshot only records the data already written to the virtual disks. None of the data in memory or pending I/O operations will be captured in the snapshot. As a result, this type of snapshot does not guarantee file system or application consistency, and you may not be able to restore virtual machines with crash-consistent snapshots. Crash-consistent snapshots are recommended for non-database operating systems and applications, such as file servers, DHCP servers, and print servers.

File-system consistent snapshot

A file-system consistent snapshot records all data in memory and pending I/O operations, in addition to the data on the virtual disks. Before a file-system consistent snapshot is taken, the file system on the guest operating system is quiesced and all file system cache data in memory and pending I/O operations are flushed to the hard drive. However, note that data recorded in file-system consistent snapshots may not be as complete as those of application-consistent snapshots. File-system consistent snapshots are recommended for database operating systems and applications such as SQL, Oracle, and Exchange.