After production has been running on the R2 side, the quickest way to give the primary-site hosts immediate access to their original R1 devices is the SRDF resume operation. resume instantaneously returns the devices to their normal R1 personality and re-enables host read/write I/O to them while marking the corresponding tracks on the remote R2 side as invalid. Replication then recommences in the normal R1 → R2 direction; no copy-back of R2 data is required beforehand, so the hosts do not have to wait for any data transfer to complete.

A. Update – Copies all invalid tracks from R2 back to R1; hosts cannot access R1 until the copy finishes.

B. Fallback – Run only after update completes; still requires the full R2 → R1 transfer first.

C. Failover – Makes R2 read/write and R1 write-disabled; moves production away from, not back to, the primary site.

1. Dell EMC Solutions Enabler SRDF CLI Product Guide v9.1

“Recovery procedures – Option 2: Return production without copying back

” pp. 166-168 (resume description).

2. Dell EMC PowerMax & VMAX All Flash SRDF Best Practices TechBook

Doc ID H17614.5

§7.3 “resume – rapid restoration of R1 access.”

3. Dell EMC PowerMaxOS 10 SRDF Concepts & Operations

White Paper

§5.4

p. 54 “resume: re-establishes R1/R2 relationship; host I/O resumes immediately on R1.”