Xsan Help: Tips for avoiding unexpected hardware or performance issues

Metadata Storage Requirements

To estimate the amount of space required for Xsan volume metadata, you can assume that 10 million files on a volume will require roughly 10 gigabytes of metadata on the volume's metadata storage pool.

Use Matching Fibre Channel Optical Transceivers

Mismatched optical transceivers (GBICs) can cause Fibre Channel communication errors and degrade SAN performance. To ensure good performance, use identical transceivers (same manufacturer and model number) on both ends of your Fibre Channel cables.

Switching a Controller's Ethernet Interface

On a controller with more than one Ethernet interface, you choose the interface that Xsan uses by choosing from the "Access the SAN via" pop-up menu in the controller information sheet in Xsan Admin.

To switch to a different interface, you must unmount and stop all hosted volumes and restart the controller to be sure its volumes are hosted on the new interface.

To change the Ethernet interface a controller uses:
1. Unmount the volumes hosted by the controller on all clients.
2. Stop the volumes.
3. Choose the new Ethernet interface. (In Xsan Admin, select the controller or SAN in the SAN Components list, click Setup, and click Computers. Then double-click the controller in the computer list and choose the new interface from the "Access the SAN via" pop-up menu, click OK, and click Save.)
4. Restart the controller.
5. Start and mount the volumes.

Add LUNs That Match the Smallest Existing LUN

If you want to increase the capacity of an existing storage pool by adding new LUNs, be sure to add LUNs that are the same size as the smallest LUN already in the storage pool.

To check the sizes of the LUNs already in a storage pool:

Open Xsan Admin, select the SAN or controller in the SAN Components list, click Setup, then click Storage.

A Client Can't Access a Volume After Fibre Channel Reconnection

If a client loses its Fibre Channel connection to the SAN (because a cable is unplugged, for example), the client might not recognize LUNs in an Xsan volume after the connection is restored. In this case, restart the client to remount the SAN volume.

To check if a computer is seeing Xsan volume LUNs:

Open Disk Utility on the computer and look for the LUNs in the list of disks and volumes.

You can also check for accessible LUNs from the command line using the "cvlabel -l" or "diskutil list" command in Terminal.

If errors persist, restart all SAN devices; begin with Xserve RAID systems, continue with SAN controllers, and finally restart all clients.

Weekly System Maintenance Scripts Can Affect SAN Performance

If client computers experience simultaneous problems with SAN performance (dropped video frames, for example), some system activity might be using needed resources. In particular, if all clients experience dropped frames at around 4:30 AM on Saturdays, it is probably due to the weekly system maintenance scripts.

One script in particular, which rebuilds the locate database, can have a noticeable impact on file system performance.

To disable the scripts:

Disable the script that runs "locate.updatedb" in /etc/weekly, or disable all the weekly maintenance scripts by commenting out the "periodic weekly" command in /etc/crontab.