Exam E20-393 topic 1 question 180 discussion

Correct B

The technology used for snapshots of both block and file resources in Dell EMC Unity is called redirect on write (ROW). With redirect on write, new writes to snapped storage resources or their snapshots are redirected to a new location in the same pool, and pointers are updated to point to the new location

Answer is B: "Snapshots of storage resources (block LUNs, file systems, and VMware Datastores) are architected using Redirect on Write technology. This architecture avoids a performance penalty that Copy on First Write technology has when existing data is changed. With Redirect on Write technology, when a snapshot is taken, the existing data on the storage object remains in place and provides the snapshot point-in-time view of the data. Production data access also uses this view to read existing data. Another benefit of Redirect on Write is that no storage resource is needed to create a snapshot. With Copy on First Write technology, a storage resource had to be reserved to hold original data that changed to preserve the point-in-time view. As its name implies, with Redirect on Write technology, when writes are made to the storage object, those writes are redirected to a new location allocated as needed from the parent pool in 256 megabyte stripes. New writes are stored in 8 kilobyte chunks on the newly allocated stripe. Reads of the new writes are serviced from this new location as well."

Correct D