Introducing ZFS snapshots

From the ZFS documentation :

“Snapshots with ZFS are similar to snapshots with Linux LVM. A snapshot is a first class read-only filesystem. It is a mirrored copy of the state of the filesystem at the time you took the snapshot. Think of it like a digital photograph of the outside world. Even though the world is changing, you have an image of what the world was like at the exact moment you took that photograph. Snapshots behave in a similar manner, except when data changes that was part of the dataset, you keep the original copy in the snapshot itself. This way, you can maintain persistence of that filesystem.

You can keep up to 2^64 snapshots in your pool, ZFS snapshots are persistent across reboots, and they don't require any additional backing store; they use the same storage pool as the rest of your data. Creating snapshots is near instantaneous, and they are cheap. However, once the data begins to change, the snapshot will begin storing data. If you have multiple snapshots, then multiple deltas will be tracked across all the snapshots. However, depending on your needs, snapshots can still be exceptionally cheap.”