Hp XP P9500 Storage User Manual download pdf (Page 41)

Determining required number of ports

The data transfer speed of your Cnt Ac-J ports must be greater than peak write-IOPS. This means

that you must dedicate the number of ports to a Cnt Ac-J pair that will be able to handle the peak

IOPS generated by your production system. The minimum number of ports for a Cnt Ac-J system is

two.

To determine the required number of initiator and RCU target ports

1. Measure the write workload you want to replicate on your production system. When you

measure write-workload, IOPS is also provided. (See “Measuring write-workload” (page 19)

for more information.)

2. Using peak IOPS and the maximum IOPS for a P9500 fibre-channel port (70,000), calculate

the number of ports your Cnt Ac-J system requires.

Peak IOPS / 70,000

For example: if your performance monitoring software shows peak IOPS at 280,000, then

the calculation would be:

280,000 / 70,000 (max. IOPS per port) = 4.

This example shows that four ports are required for the measured peak IOPS.

Cable length and switch requirements

Multimode or single-mode optical fiber cables are required on primary and secondary systems.

The type of cable and number of switches depends on the distance between primary and secondary

sites.

• 0 to 0.5 km: multimode optical shortwave fiber cables are required.

• 0.5 km to 1.5 km (1,640 to 4,920 feet): multimode shortwave fibre-channel interface cables

are required; one switch is required, two maximum.

• 1.5 km to 10 km: single optical long-wave fiber cables are required.

• 10 km to 30 km (6.2 to 18.6 miles): single-mode long-wave fibre-channel interface cables

are required; one switch is required, two maximum.

• Greater than 30 km (18.6 miles): approved third-party channel extender products and

telecommunications lines are required.

This information is illustrated in Figure 8 (page 42).

Additional switches

When the initiator port on the primary system sends data to the secondary system, the fibre-channel

protocol accommodates a certain number of un-acknowledged frames before the sender must stop

sending. These are known as buffer credits. As fibre-channel frames are sent out, available buffer

credits are exhausted. As acknowledgments come back, the supply of buffer credits is replenished.

Because it takes longer for acknowledgments to return as distance increases, exhausting the supply

of buffer credits becomes increasingly likely as distance increases.

Adding fibre-channel switches on either end of the replication network provides the additional

credits necessary to overcome buffer shortages due to the network latency.

Cable length and switch requirements 41

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Hp XP P9500 Storage User Manual Page 41