Isl Oversubscription; Isl Oversubscription; Device Locality - HP 316095-B21 - StorageWorks Edge Switch 2/24 Planning Manual

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
Depending on fabric performance requirements and cost, there are several options
to solve ISL oversubscription problems, including:
SAN High Availability Planning Guide
illustrates ISL oversubscription. Two NT servers, each with maximum
Storage
1 Gbps ISL
NT Server 2
(100 MBps Max)
Employ device locality — NT server 1 and its associated storage device can
be connected through one director. NT server 2 and its associated storage
device can be connected through the other director. As a result, minimal
traffic flows across the ISL between directors and the congestion problem is
mitigated. For additional information, refer to
Planning Considerations for Fibre Channel Topologies
200
150
100
50
0
1
5 10
Time (Sec)
"Device
1 Gbps ISL
NT Server 1
NT Server 2
15 20 25
Locality" on page 102.
101