HP Surestore 64 FW 05.01.00 and SW 07.01.00 HP StorageWorks SAN High Availabil - Page 75

ISL bandwidth limitation

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Planning Considerations for Fibre Channel Topologies ■ Although the B_Port connection (ISL) between the director and switch is a 1.0625 Gbps serial connection, burst transmissions from multiple FC-AL devices are multiplexed and buffered (the link BB_Credit value is eight), and may coexist in the link. Therefore, the sum of the bandwidths of all devices contending for B_Port access should not exceed 1.0625 Gbps. Exceeding the total bandwidth may result in degraded performance, as shown in Figure 32. Arbitration Cycle Idle Burst Data (D1) Burst Data (D2) Burst Data (D3) Burst Data (S1) H_Ports D1 (30 MBps) S1 (10 MBps) D2 (30 MBps) D3 (30 MBps) ISL (1 Gbps) B_Port 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. SAN High Availability Planning Guide 75

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Planning Considerations for Fibre Channel Topologies
75
SAN High Availability Planning Guide
Although the B_Port connection (ISL) between the director and switch is a
1.0625 Gbps serial connection, burst transmissions from multiple FC-AL
devices are multiplexed and buffered (the link BB_Credit value is eight), and
may coexist in the link. Therefore, the sum of the bandwidths of all devices
contending for B_Port access should not exceed 1.0625 Gbps. Exceeding the
total bandwidth may result in degraded performance, as shown in
Figure 32
.
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.
(30 M ps)
B
D
1
S
1
(10 M ps)
B
D
2
(30 M ps)
B
D
3
(30 M ps)
B
ISL
(1 Gbps)
H_Ports
B_Port
Arbitration Cycle
Idle
Burst Data (D )
1
Burst Data (D )
2
Burst Data (D )
3
Burst Data (S )
1