Table of Contents
Advertisement
Planning Considerations for Fibre Channel Topologies
3
McDATA Products in a SAN Environment - Planning Manual
3-32
•
Read/write mixture - Although application I/O is typically a
mixture of read and write operations, some applications are very
biased. For example, video server applications are almost 100%
read intensive, while real-time video editing applications are
mostly write intensive. Read operations typically take less time
than write operations, therefore storage devices for a
read-intensive application usually wait for data transfer. As a
consequence, read-intensive applications typically require high
bandwidth to the device.
•
Type of data access - When an application requires data, access to
that data is random or sequential. For example, e-mail server
activity is random access, while seismic data processing for the oil
and gas industry is sequential access. Sequential data access
typically takes less time than random data access, therefore
sequential-access applications usually wait for data transfer. As a
consequence, sequential-access applications typically require
high bandwidth to the device.
•
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
Oversubscription. For information about application I/O (in IOPS) and
fabric performance problems due to port contention, refer to
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.
oversubscription.
Figure 3-12
illustrates ISL
ISL
Device
Advertisement
Table of Contents
