FW V06.XX/HAFM SW V08.02.00 HP StorageWorks SAN High Availability Planning Guide (AA-RS2DD-TE, July 2004)

Table Of Contents

Planning Considerations for Fibre Channel Topologies

77SAN High Availability Planning Guide

Figure 32: ISL bandwidth limitation

Three 30-megabyte per second (MBps) tape drives and one 10-MBps server are

attached to a switch. Each device uses only a portion of the bandwidth of its

respective H_Port connection. Each H_Port connection illustrates four arbitration

cycles (each cycle won by a single device), one cycle of burst data transmission,

and three idle cycles. The B_Port connection to a director (ISL) transmits

multiplexed burst data from all four devices, for which the summed bandwidths

equal the 1.0625 Gbps capacity of the link. Therefore, connection of additional

devices to the switch adversely impacts B_Port performance.

Server Consolidation

Providing fabric connectivity for multiple low-bandwidth servers (Windows NT

or UNIX-based) by attaching them individually to an expensive Fibre Channel

director is not a cost-effective solution. A practical solution is to consolidate the

servers on an inexpensive loop switch, and then connect the switch to a single

director or edge switch E_Port.

Figure 33 illustrates the consolidation of ten servers (using two unmanaged hubs)

through one B_Port connection to a director. Each server has a 10-MBps

bandwidth, therefore, the sum of the bandwidths of all consolidated servers equals

the B_Port bandwidth of 1.0625 Gbps. Connecting another server to the switch

would exceed the B_Port capability and adversely impact director-to-switch link

performance. Other devices (such as tape drives) should not be connected to a

switch used for server consolidation.

(30 M ps)BD

(10 M ps)B

(30 M ps)B

ISL (1 Gbps)

H_Ports

B_Port

Arbitration Cycle

Idle

Burst Data (D )

Burst Data (S )