Snapshotting

Snapshotting is the process of capturing a point-in-time representation of a data volume, filesystem, virtual machine, or database. A snapshot records the state of the data at the moment it is created and is often implemented using copy-on-write or redirect-on-write techniques to minimize space usage. Depending on the system, a snapshot can be crash-consistent (relying on the OS to ensure data integrity after a crash), or application- or quiesced-consistent, which may require pausing or flushing in-flight operations to ensure a clean state. In virtualization, snapshots may include the VM's memory and CPU state; in filesystems and storage arrays, they typically capture metadata and blocks.

There are several snapshot types. Filesystem or volume snapshots create a point-in-time image of stored data; VM snapshots preserve a VM’s state for later restoration; database snapshots may be taken at transaction boundaries or with specialized agents to ensure consistency. Snapshots are often read-only, though some systems allow writable clones that share underlying data.

Common uses include backups and disaster recovery, testing and development, and cloning environments for staging. Snapshots enable rapid restores to a known good state and can enable rollbacks after software updates. Many systems support incremental or delta snapshots, storing only changes since the previous snapshot to save space.

Key considerations include storage consumption, performance impact during creation, and the need for proper retention policies to prevent snapshot sprawl. Restores should be validated, and consistency requirements should guide whether quiescing is needed. Notable implementations include ZFS, Btrfs, LVM, Windows Shadow Copy, and cloud provider services such as AWS EBS snapshots and Google Persistent Disk snapshots.