HP StorageWorks MSA 2/8 HP StorageWorks Fabric OS Procedures V3.1.x/4.1.x User - Page 160
Frequently Asked Questions, Q: What is a PID?
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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