Frequently Asked Questions - HP StorageWorks MSA 2/8 - SAN Switch User Manual

Updating Switches to the Core PID Addressing

Frequently Asked Questions

Q: What is a PID?
A: A PID is a Port Identifier. PIDs are used by the routing and zoning services in
Fibre Channel fabrics to identify ports in the network. They are not used to
uniquely identify a device; the World Wide Name (WWN) does that.
Q: What Situations Can Cause a PID to Change?
A: Many scenarios cause a device to receive a new PID. For example, unplugging
the device from one port and plugging it into a different port (this might happen
when cabling around a bad port, or when moving equipment around). Another
example is changing the Domain ID of a switch, which might be necessary when
merging fabrics, or changing compatibility mode settings.
Q: Why do some devices handle a PID change well, and some poorly?
A: Some older device drivers behave as if a PID uniquely identifies a device.
These device drivers should be updated, if possible, to use WWN binding instead.
A device's WWN never changes, unlike its PID. PID binding creates problems in
many routine maintenance scenarios and should always be avoided. Fortunately,
very few device drivers still behave this way, and these are expected to be updated
as well. Many current device drivers enable binding by PID. Only select this
method if there is a compelling reason, and only after you have evaluated the
impact of doing so.
Q: Must I schedule downtime for my SAN to perform the PID update?
A: Only if you do not have dual-fabrics or have devices that bind by PID.
Q: Must I stop all traffic on the SAN before performing the update?
A: If you are running dual-fabrics with multi-pathing software, you can update
one fabric at a time. Move all traffic onto one fabric in the SAN, update the other
fabric, move the traffic onto the updated fabric, and update the final fabric.
Without dual-fabrics, stopping traffic is highly recommended. This is the case for
many routine maintenance situations, so dual-fabrics are always recommended for
uptime-sensitive environments.
Q: How can I avoid having to change PID formats on fabrics in the future?
A: The core PID format can be proactively set on a fabric at initial installation.
The update could also be opportunistically combined with any scheduled outage.
Setting the format proactively far in advance of adoption of higher port count
switches is the best way to ensure administrative ease.
160 Fabric OS Procedures Version 3.1.x/4.1.x User Guide