A snapshot volume is a special type of volume that presents all the data that was in the volume at the time the snapshot was created. This means you can back up that volume without having to worry about data being changed while the backup is going on, and you don’t have to take the database volume offline while the backup is taking place.
Niclas has posted a nice howto about consistent MySQL backups using Solaris UNIX ZFS snapshots:
In this article I will show you how to install MySQL on a ZFS file system and supply you with a script to make consistent snapshots of the databases. This script may not be 100% fit for busy sites but for most smaller places I think it is perfect.