ABSTRACT
This chapter discusses the various snapshot techniques that can be used in data protection and their applicability. The copy on first write (COFW) snapshot technique is designed to minimize the amount of storage capacity required to take a snapshot of a filesystem. Copy on first access (COFA) is a snapshot process typically associated with generating clones of data, typically at the volume/LUN level. These initially look quite similar to a COFW snapshot, in that the snapshot copy starts as a set of pointers back to the original content that was snapshot. A single snapshot by itself provides a single point in time of data protection, but snapshots become particularly more useful when people consider the speed at which they can be generated and how space efficient they are. This allows storage administrators to offer considerably tighter and more business compatible service-level agreements (SLAs) regarding RPO and RTO than a traditional backup strategy.
