Isl Oversubscription - HP StorageWorks 64 - SAN Director Switch Planning Manual

Prior to fabric design, application I/O profiles should be estimated or established
that classify the application bandwidth requirements. Bandwidth consumption is
classified as light, medium, or heavy. These classifications must be considered
when planning ISL and device connectivity. For information about application I/O
(in Gbps) and fabric performance problems due to ISL connectivity, refer to
Oversubscription." For information about application I/O (in IOPS) and fabric
performance problems due to port contention, refer to
on page 101.

ISL Oversubscription

ISL oversubscription (or congestion) occurs when multiplexed traffic from several
devices is transmitted across a single ISL. When an ISL is oversubscribed, fabric
elements use fairness algorithms to interleave data frames from multiple devices,
thus giving fractional bandwidth to the affected devices. Although all devices are
serviced, ISL and fabric performance is reduced.
Figure 41
I/O of 100 MBps, are contending for the bandwidth of a single ISL operating at
1.0625 Gbps. In addition to data, the ISL must also transmit Class F traffic
internal to the fabric. When operating at peak load, each NT server receives less
than half the available ISL bandwidth.
NT Server 1
(100 MBps Max)
Figure 41: ISL oversubscription
SAN High Availability Planning Guide
illustrates ISL oversubscription. Two NT servers, each with maximum
Storage
1 Gbps ISL
NT Server 2
(100 MBps Max)
Planning Considerations for Fibre Channel Topologies
"Device Fan-Out
200
150
100
50
0
1
5
10
Time (Sec)
Ratio"
1 Gbps ISL
NT Server 1
NT Server 2
15 20 25
"ISL
99