HP XP P9500 Storage - Manual (Page 12)

Snapshot data storage methods
You can use the Copy-On-Write (COW) method or the Copy-After-Write (CAW) method to store
snapshot data. In the COW method, when the P-VOL snapshot data is acquired, the status changes
to the write completion status. In the CAW method, when the P-VOL snapshot data is written, the
status changes to the write completion status. The CAW method wait time is shorter than that of
the COW method.
The following figure illustrates the CAW method.
The following figure illustrates the COW methods.
12 Overview of Fast Snap