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400-007 · Question #99

Company XYZ is planning to deploy primary and secondary (disaster recovery) data center sites. Each of these sites will have redundant SAN fabrics and data protection is expected between the data…

The correct answer is B. VSANs must be routed between sites to isolate fault domains and increase overall availability. C. Synchronous data replication must be used to meet the business requirements. At 160 km, synchronous SAN replication is technically feasible and provides guaranteed RPO, while VSAN routing between sites isolates fault domains to prevent cross-site failures.

Designing Network Infrastructure

Question

Company XYZ is planning to deploy primary and secondary (disaster recovery) data center sites. Each of these sites will have redundant SAN fabrics and data protection is expected between the data center sites. The sites are 100 miles (160 km) apart and target RPO/RTO are 3 hrs and 24 hrs, respectively. Which two considerations must Company XYZ bear in mind when deploying replication in their scenario? (Choose two.)

Options

  • ATarget RPO/RTO requirements cannot be met due to the one-way delay introduced by the
  • BVSANs must be routed between sites to isolate fault domains and increase overall availability.
  • CSynchronous data replication must be used to meet the business requirements.
  • DAsynchronous data replication should be used in this scenario to avoid performance impact in the
  • EVSANs must be extended from the primary to the secondary site to improve performance and

How the community answered

(34 responses)
  • A
    6% (2)
  • B
    56% (19)
  • D
    26% (9)
  • E
    12% (4)

Why each option

At 160 km, synchronous SAN replication is technically feasible and provides guaranteed RPO, while VSAN routing between sites isolates fault domains to prevent cross-site failures.

ATarget RPO/RTO requirements cannot be met due to the one-way delay introduced by the

A 160 km distance introduces only approximately 0.8 ms of one-way propagation delay, which is negligible and poses no obstacle to achieving a 3-hour RPO or 24-hour RTO target.

BVSANs must be routed between sites to isolate fault domains and increase overall availability.Correct

Routing VSANs between sites (rather than extending a single VSAN across both locations) creates distinct fault domains, so a fabric failure, misconfiguration, or RSCN storm at the primary site cannot propagate to the secondary site, preserving disaster recovery availability.

CSynchronous data replication must be used to meet the business requirements.Correct

At 160 km, the round-trip fiber propagation latency is approximately 1.6 ms, which falls well within the acceptable threshold for synchronous block replication (typically under 5 ms RTT), making synchronous replication technically viable and ensuring a zero RPO that comfortably meets the 3-hour requirement.

DAsynchronous data replication should be used in this scenario to avoid performance impact in the

Asynchronous replication reduces write latency impact on the primary site but introduces a replication lag window and potential data loss; since synchronous replication is technically feasible at this distance, choosing asynchronous trades data protection for a performance benefit that is not required here.

EVSANs must be extended from the primary to the secondary site to improve performance and

Extending the same VSAN from the primary to the secondary site merges fault domains across geographic locations, meaning a fabric event at one site directly affects the other and undermines the isolation goal of a disaster recovery architecture.

Concept tested: Multi-site SAN replication strategy and VSAN fault isolation

Source: https://www.cisco.com/c/en/us/td/docs/storage/san_solutions/sanops/SAN_Operations.html

Topics

#data center replication#SAN#RPO/RTO#VSAN design

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