Specifications

4
Implementing SAN Internetworking Solutions
4-37
Implementing SAN Internetworking Solutions
• Reliability - Local storage traffic requires high-reliability
communication and is intolerant of data loss, out-of-order packet
receipt, or data retransmission. WANs typically provide best-
effort communication service and rely on upper-level protocols
for end-to-end transport.
Because of these differences, a protocol conversion approach is
usually required to integrate Fibre Channel SAN traffic over a
geographically-dispersed network. Refer to SAN Extension Transport
Te c h n o lo g i e s for detailed information about native FCP distance
extension or protocol conversion.
Other BC/DR requirements vary, depending on budget, data type,
data volume, business situation, and SAN applications. Analyze and
understand these business requirements prior to selecting an
operational mode (described in Extended-Distance Operational Modes)
and transport technology (described in SAN Extension Transport
Te c h n o lo g i e s ) that best support the SAN distance-extension strategy. In
particular, consider:
• Data priority - Not all data is critical to immediate business
resumption. Prioritize and categorize data as mission-critical,
secondary, or only to be retained for legal purposes.
• Recovery time objective (RTO) - The RTO is the time required to
restore the data and applications following an outage or disaster.
The loss of revenue from suspended business operations drives
this objective.
• Recovery point objective (RPO) - The RPO is the time between
backup points and defines how far out of date a backup copy can
be after a failure. The data rate of change and cost of destroyed
data (between the last backup and a disaster) drive this objective.
• Distance - The distance between a data center and replication site
is proportional to RTO and RPO times. As distance between sites
increases, time required to perform backup and restore operations
also increases.
Extended-Distance
Operational Modes
A primary component of business continuance and disaster recovery
is remote data replication to an alternative safe location. Extended-
distance operational modes are: