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Mainframe Solutions

FICON Dynamic Channel Path Management (DCM) 2013

by Dr.Steve.Guendert on ‎10-22-2013 03:03 AM (4,735 Views)

My last blog posting discussed the 23 July 2013 set of IBM System z announcements, and how those announcements encourage channel consolidation by IBM System z customers.   One of the items I briefly covered was Dynamic Channel  Path Management (DCM) for FICON.  This blog post will discuss DCM in more detail, and make the case why you should seriously consider implementing DCM.


DCM support for native FICON channels was originally introduced in z/OS V1.11 with support for a single, intermediate FICON switching device between the FICON channel and storage control units.  The recent IBM z/OS V 2.1 announcement significantly enhanced DCM for FICON.  In z/OS V2.1, DCM was enhanced to support FICON channel path connections through two intermediate FICON switching devices, i.e. with z/OS V 2.1, DCM for FICON now supports cascaded FICON configurations.


This really is an important step in the evolution of System z I/O architectures.  With DCM for FICON now supporting cascaded configurations, it will be much easier to use a smaller number of channels (channel consolidation) and optical fiber connections for FICON I/O, particularly for multi-site installations that rely on cascaded FICON.  Remember, z/OS V2.1 also introduced support for up to 24K subchannels per FICON channel.


Dynamic Channel Path Management (DCM) provides the ability to have the system automatically manage FICON I/O paths connected to DASD subsystems in response to changing workload demands. 


According to the IBM Whitepaper “FICON DCM for Systems Programmers”, the objectives for FICON DCM are fivefold:


  1. Simplify I/O configuration planning and definition
  2. Reduce the customer skills required to manage z/OS
  3. Dynamically balance I/O channel resources
  4. More efficient use of channel resources
  5. Enhance availability


DCM does this by allowing customers to identify FICON channels they wish to be “managed”. Managed channels are channels which are not assigned to any specific control unit by the customer. Instead, these channels are viewed as a pool of FICON channels that may be assigned dynamically to control units at the discretion of the system. By assigning channels to the pool of managed channels, the system is able to respond to peaks in control unit demand for I/O channel bandwidth. In addition, this reduces the complexity of defining the I/O configuration: the end user is no longer required to define a configuration that will adequately address any variations in workload. This allows them to specify a much “looser” configuration.


One of the things that is readily apparent to me as I meet with many of you around the world is how over configured I/O architectures are.  Yes, you absolutely need to plan for redundancy in the event of some type of failure somewhere in the configuration.  But there is a difference between planning for redundancy, and overkill.  And when your configuration has 2-3x the number of FICON channels configured than what you actually use during periods of peak production workloads, you have overkill along the lines of what the USA and USSR had with their nuclear arsenals back in the 1980s.


FICON channels have improved in terms of I/O performance remarkably over the last 5 years, particularly when implementing zHPF.  Yet, most of your configurations have changed very little to take advantage those improvements, or improvements such as DCM or the improved channel load balancing algorithms.  We’re still doing the same ol same ol' architectures.  When we upgrade to a new processor with new channels, we still get the same exact number of channels.  No channel consolidation at all.  What boggles my mind even further is how many end user installations have not even taken the time to do some form of testing and analysis to see if, and how they could consolidate their FICON channels, and how DCM and the other enhancements may benefit them.


I’d encourage you to at a minimum take a long, serious look at FICON DCM.  Do some analysis work and see how it would work in your environment. Look at your channels and do a study of how you could consolidate channels yet still keep sufficient redundancy. Reagan and Gorbachev got rid of some overkill, you could too and likelysave your organization some serious money and make your job easier too.



Dr. Steve