SVC and Storwize V7000 Release 6.3: WWPN limits

IBM recently released a new version of firmware for the SAN Volume Controller and Storwize V7000.  This is known as release 6.3 and continues the tradition of two major updates per year, each adding significant new functions.

So the 6.3 release notes for both Storwize V7000 and SVC listed the following new feature:

• Support for 4096 host WWPNs

Since I blithely listed this feature in a recent post I have received lots of emails asking exactly what it means, so I thought I had better explain.

The IBM SVC and Storwize V7000 have always had very clearly published maximum capabilities such as the ones listed here for Storwize V7000 release 6.3 and here for SVC release 6.3.

Most of these numbers are very high and few customers actually approach these maximums.   The main issue I am seeing for some of our larger AIX customers is this one:

• Total Fibre Channel ports (WWPNs) per I/O group​:  512

The reason this can become an issue is the combination of NPIV and AIX Live Partition Mobility.  NPIV allows one physical HBA to be shared among multiple operating system instances, each one believing it has exclusive access to the HBA with each one allocated its own unique WWPNs.  Suddenly a single HBA which used to present just one WWPN through the SAN to the SVC, can now present vast numbers of them.   In addition AIX Live Partition Mobility (which lets you move AIX operating systems between LPARs on the fly) needs additional pre-configured WWPNs defined on the target LPAR to support the move.   This further increases the quantity of  WWPNs that need to be defined to the SVC (one easy way to spot NPIV generated WWPNs is they normally start with the letter C).

So the bottom line is that IBM needs to make this limit bigger and SVC and Storwize V7000 6.3 code contains the necessary architectural changes to allow this.   The first phase is to start potentially supporting up to 2048 WWPNs per I/O group although clearly based on the initial version of the release notes, the long-term plan is to support 4096.

But there is a problem and it has nothing to do with the SVC or Storwize V7000. The problem is that there are certain SAN configurations which may have issues with these large numbers of WWPNs (mainly around older SAN switches not having the CPU power for the switch fibre channel name-server and login-server to handle vast numbers of WWPNs coming out of one HBA).

So what should you do if you need to push the limits?

Contact your IBM Pre-Sales support and ask for a SCORE request to be opened (also known as an RPQ).  You will need to detail your current SAN configuration (especially switch models and firmware levels) so that SVC development can ensure you won’t overwhelm your switches.  It will also allow our development team to learn how many clients our there need this support.   All approvals will include a requirement to upgrade to release 6.3, so you should include this in your planning.

Any questions?   Feel free to leave a comment or send me a tweet or an email.

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