Specifications

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McDATA Products in a SAN Environment - Planning Manual
Planning Considerations for Fibre Channel Topologies
• I/O block size - The third characteristic of application I/O is data
block size, which typically ranges from two kilobytes (KB) to over
one megabyte (MB). Applications that generate large blocks of
data require high bandwidth to the device.
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 ISL
Oversubscription. For information about application I/O (in IOPS) and
fabric performance problems due to port contention, refer to Device
Fan-Out Ratio.
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 3-12 illustrates ISL
oversubscription.
Figure 3-12 ISL Oversubscription
NT Server 1
(100 MBps Max)
1 Gbps ISL
Storage
NT Server 2
(100 MBps Max)
T
M
T
M
1
5
10 15
20
25
0
100
150
200
Time (Sec)
Bandwidth (MBps)
50
1 Gbps ISL
NT Server 1
NT Server 2