SAN troubleshooting: Port/device mismatch
SAN devices come in two main flavors and mixing them up is one of the most common causes of problems with a SAN. It can be especially difficult to troubleshoot because the first line of diagnostics, the port lights on the switch, won't show the problem.
Devices, such as HBAs, can be either switch fabric (FC-SW) or arbitrated loop (FC-AL). The problem comes when the device thinks it is one and the port on the switch thinks it is the other. While fabric devices can communicate with loop devices, it often doesn't work the other way around. This is particularly frustrating because the port light for the port the device is attached to will turn green, indicating a successful connection, when in fact the device and the port aren't communicating.
To check for this kind of mismatch, log into the switch and see if the port is set for FC-AL or FC-SW. Once you figure out what is going on, the fix is a matter of resetting the port and rebooting the system.
A brief description of troubleshooting SANs can be found at the VALUEVAD web site at: http://www.valuevad.com/.%5Cnews%5CIMnews40.htm
Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.
Did you like this tip? Whether you did or not, why not let us know. Drop us an email and sound off.
Storage Area Networks: Designing and Implementing a Mass Storage System, 1/e
Author : Ralph Thornburgh and Barry Schoenborn
Publisher : Prentice Hall
Published : Sep 2000
Every month, enterprises require more information, delivered faster, with greater reliability--and traditional data storage methods no longer suffice. Enter the Storage Area Network (SAN), which can store enormous amounts of data, serve it at lightning speed, scale to meet accelerating growth, and deliver unprecedented reliability. Now, there's a complete guide to SAN technology for every IT professional and decision-maker. Storage Area Networks covers it all: key concepts, components, applications, implementation examples, management, and much more.