A volume snapshot captures the data that exists in a volume at a given point in time. As such, VxVM does not have any knowledge of data that is cached in memory by the overlying file system, or by applications such as databases that have files open in the file system. Snapshots are always crash consistent, that is, the snapshot can be put to use by letting the application perform its recovery. This is similar to how the application recovery occurs after a server crash. If the fsgen volume usage type is set on a volume that contains a mounted Veritas File System (VxFS), VxVM coordinates with VxFS to flush data that is in the cache to the volume. Therefore, these snapshots are always VxFS consistent and require no VxFS recovery while mounting.

For databases, a suitable mechanism must additionally be used to ensure the integrity of tablespace data when the volume snapshot is taken. The facility to temporarily suspend file system I/O is provided by most modern database software. The examples provided in this document illustrate how to perform this operation. For ordinary files in a file system, which may be open to a wide variety of different applications, there may be no way to ensure the complete integrity of the file data other than by shutting down the applications and temporarily unmounting the file system. In many cases, it may only be important to ensure the integrity of file data that is not in active use at the time that you take the snapshot. However, in all scenarios where application coordinate, snapshots are crash-recoverable.