Spectrum Virtualize NPIV and Host Connectivity
A while ago I wrote this post as an introduction to the Spectrum Virtualize NPIV feature. In this follow-up post I thought I would focus more on host connectivity and the effects of NPIV. You can watch a quick review of the NPIV feature in this IBM Systems Rockstar video:
NPIV has 3 modes:
1. Disabled - this mode means that hosts cannot connect to the virtual World Wide Port Names (WWPNs) on the Spectrum Virtualize cluster, regardless of the fabric zoning
2. Transitional - this mode means hosts can connect to either the physical or virtual WWPNs on the cluster. If a host is zoned to both, it will connect to both. Transitional mode is meant to only be used while you are migrating to NPIV mode and rezoning your hosts to the virtual WWPNs. It is not meant to be used permanently or even long-term.
3. Enabled - this means hosts can only connect to the virtual WWPNs. If they are zoned to the physical WWPNs the connection will be listed as 'blocked' in the device connectivity listing.
Transitional mode is intended for moving a cluster that previously did not have NPIV enabled to enabling NPIV. It takes time to rezone hosts to use only the virtual WWPNs. During the transition, care must be taken to not allow any host to be zoned to both the virtual and physical WWPNs on the cluster. If a host is zoned like that, it will connect to both ports and the path count and connection count will be doubled. Multipathing can have problems with too high of a path count and while I have not seen it often, I have seen large clusters with a high host count run out of connections.
Here is a cluster that has NPIV disabled. You can see in the GUI screenshot that Host I/O is not permitted on the WWPNs that are listed as 'Yes' in the Virtualized column.
You can also run lstargetportfc and get similar output. Note that host_io_permitted is only 'yes' for WWPNs that are not virtualized.