Snapshots have practically no impact on system performance and can be taken for each filesystem while applications are running. They consume minimal space, according to the actual differences between the filesystem and the snapshots, or between the snapshots, in 4K granularity. By default, snapshots are read-only, and any attempts to change the contents of a read-only snapshot returns an error message. It is possible to create a writable snapshot or update an existing snapshot to be writable. However, a writable snapshot cannot be updated to be read-only.