IBM Z9, Planning Manual

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does not require any control unit involvement. Busies are handled by the ESCON or
FICON Director. Therefore, the control unit is effectively relieved of handling busy
conditions and is able to handle more I/O requests. Because switch port busies
require fewer trips over the ESCON or FICON connection link, they are less
sensitive to increased distances than control unit busy encounters.
MIF Channel Sharing: Moves busy management back into the channel subsystem,
providing the most efficient management of busy conditions. Because multiple LPs
access the same physical channel, I/O attempts are concentrated at the channel
level. A CU busy or a switch port busy is handled as a channel busy.
Planning for Concurrent Data Transfer: Before you can consolidate channels,
you must be aware of the channel requirements of the particular control units you
are configuring. Table 2-4 shows the maximum recommended ESCON channels for
a single system going to a control unit. The number of channels needed is
independent of the number of LPs on a system. The number of channels is based
on the number of concurrent data transfers the control unit is capable of. Although
the recommended number of channels satisfies connectivity and performance
requirements, additional channels can be added for availability.
Table 2-4. MIF Maximum Channel Requirements
Control Unit Type
Maximum Channels
(See note)
9343 Storage Controller
9343 D04
9343 DC4
4
4
3990 Storage Control
3990-2
3990-3
3990-6
4
4
4
3490 Magnetic Tape Subsystem
3590
3490 D31, D32, D33, D34
3490 C10, C11, C12
3490 A01
3490 A10
3490 A02
3490 A20
2
1
1
1
1
2
2
2074 Console Support Controller
2074 002 2
3174 Establishment Controller
3174 12L (SNA only)
3174 22L (SNA only)
1
1
Note: The recommended maximum channels given in this table are based on performance
and connectivity requirements and do not include channels for availability.
Understanding Examples of MIF Consolidation: The following examples provide
some general guidelines to show how MIF can help you consolidate and use
hardware resources more efficiently:
ESCON Configurations: Figure 2-9 on page 2-24 shows how four shared ESCON
channels can replace 16 unshared (dedicated or reconfigurable) ESCON channels
and use 12 fewer control unit ports.
Chapter 2. Planning Considerations
2-23