User guide

Chapter 2 Planning a Storage Area Network 33
Planning the Fibre Channel Network
Xsan uses Fibre Channel connections to:
Transfer user data between clients and data storage pools Â
Transfer metadata between metadata controllers and metadata storage pools Â
If you have connections operating below the data rate supported by your equipment
(typically 2 or 4 Gb/s), verify Fibre Channel performance and troubleshoot the fabric.
Verifying Base Fibre Channel Performance
Because the devices connected to a Fibre Channel network adjust their speed to
match the slowest device on the fabric, be sure that all connections in the fabric are
operating at the expected speed (typically 2 or 4 Gb/s).
To check Fibre Channel connection performance:
Use the management software provided with your Fibre Channel switches to test the m
performance of your Fibre Channel fabric.
If Your Fibre Channel Fabric Is Running Slower Than Expected
If your Fibre Channel fabric isn’t running at the expected speed (typically 2 or 4 Gb/s,
depending on your equipment), review the following information.
Check Cables
One faulty cable in a fabric can slow the entire network. Check all cables to make sure
they’re capable of full transmission speed. Use your switch management software to
isolate the faulty cable by checking the performance of specic connections.
Use Qualied Transceivers in Matching Pairs
Check with the manufacturers of the devices you’re connecting to your fabric to be
sure that the transceivers (GBICs) you’re using are qualied for use with their devices.
Also, use identical transceivers (same manufacturer and model number) on both ends
of each cable. Mismatched optical transceivers (even if they are separately qualied for
use with your devices) can cause Fibre Channel communication errors and degrade
SAN performance.
Check Fibre Channel Switch Port Conguration
The Request for State Change Notications (RSCN) that is generated when a client on
the SAN restarts can cause dropped frames in video streams to other clients.
To avoid interrupting SAN trac to other clients if one client restarts, check your Fibre
Channel switch documentation to see if you can congure the switch to suppress
RSCNs on initiator ports. (For example, on Qlogic switches this feature is called I/O
StreamGuard.)