Why manage logical paths?

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The ESCON and FICON® environments (the use of ESCON and FICON channels and ESCON and FICON Directors) greatly enhances the connectivity potential for control units. In addition, you can define shared channels that can request additional logical paths. However, control units can allocate only a limited number of logical paths in relation to the number of logical paths that channels can request. (See Table 1.) In configurations where channels request more logical paths than a control unit can allocate, you must manage logical paths to ensure that the I/O operations you intend take place.
Table 1. Logical path summary by control unit
Control unit Maximum physical links Logical paths per link Maximum logical paths
2105 storage controller

2105

 32 64 2048
3990 storage controller
3990-2 16 Note 1 16
3990-3 16 Note 1 16
3990-6 16 Note 2 128
9343 storage controller
9343 D04 4 64 64
9343 DC4 4 64 64
3590 magnetic tape subsystem
3590 2 64 128
3490 magnetic tape subsystem
3490 D31, D32, D33, D34 1 16 16
3490 C10, C11, C12 1 16 16
3490 A01 2 16 32
3490 A10 4 16 64
3490 A02 4 16 64
3490 A20 8 16 128
3172 interconnect controller
3172-1 2 Note 3 16
3174 establishment controller
3174 12L (SNA only) 1 Note 3 8
3174 22L (SNA only) 1 Note 3 8
Notes:
  1. 3990-2 and 3990-3 Storage Controls can have eight logical paths per side, two sides, with a minimum of one logical path per adapter.
  2. The 3990-6 Storage Control can have 64 logical paths per side, two sides, with a maximum of 32 logical paths per adapter.
  3. The 3172 Interconnect Controller and the 3174 Establishment Controller can have one logical path per logical control unit (LCU) with a maximum of eight LCUs per link.