IBM Storwize V7000, Introduction And Implementation Manual

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Chapter 9. IBM Flex System V7000 Storage Node Copy Services
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Figure 9-68 The effect of packet size (in bytes) versus the link size
Before you proceed, take a quick look at the second largest component of your
round-trip-time, that is, serialization delay. Serialization delay is the amount of time required to
move a packet of data of a specific size across a network link of a given bandwidth. This delay
is based on a simple concept: the time required to move a specific amount of data decreases
as the data transmission rate increases.
In Figure 9-68, there are orders of magnitude of difference between the different link
bandwidths. It is easy to see how 1920 errors can arise when your bandwidth is insufficient
and why you should never use a TCP/IP
ping to measure RTT for FCIP traffic.
Figure 9-68 compares the amount of time in microseconds required to transmit a packet
across network links of varying bandwidth capacity. Three packet sizes are used:
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64 bytes: The size of the common ping packet
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1500 bytes: The size of the standard TCP/IP packet
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2148 bytes: The size of a Fibre Channel frame
Remember that your path MTU affects the delay incurred in getting a packet from one location
to another, when it causes fragmentation or is too large and causes too many retransmits
when a packet is lost.