The Snapshot Process
Copy-On-Write – Disk Perspective
1. CoW Driver is loaded and Snapshot is created.
2. Write I/O comes into the storage array from the host
3. Primary (existing) blocks are copied to Snapshot area for safe
keeping
4. Pointers are updated to show snapshot change is in pool area
5. Allow Write I/O request to complete
(4) Update cache map
Cache Map
(1) CoW
(2) Write Request
Primary
(3) Move old blocks to cache
Disk
Driver
Disk Area
Pool
(5) Allow write to complete