Xsan 1.4 appears to be the Xsan we have all been waiting for. ACLs work great, Photoshop saves files on Xsan volumes without complaining from time to time, and After Effects renders without the grey blocks.
Yet, I wasn’t prepared that Xsan 1.4 requires all your MDCs to be turned on after a restart of your Xsan system.
Until now, after a complete shutdown of an Xsan system I was used to turn on the Xserve RAIDs first; then I turned on the primary MDC and activated the volume. Afterwards I started the other MDCs, then the clients, then I mounted the volume on the clients.
With Xsan 1.4 you can not activate an Xsan volume if not all of your MDCs are turned on. On each MDC there is the file /Library/Filesystems/Xsan/config/fsnameservers. It includes a list of your MDCs’ IP addresses. When all of the machines listed in here are accessible, the Xsan volume activates and mounts on specified clients. If one of these machines is turned off, you can not start an Xsan volume.
To activate your Xsan volumes, you can either start all of your MDCs. As soon as they are available, everythings works fine automatically, you don’t need to play around with config files. Or you change any setting in Xsan Admin that requires to save some settings on your current MDC. E.g. change the role of your MDC from high to medium and back to high or activate ACLs and turn them off again (or vice versa!). Save these settings, and Xsan Admin will make sure that the fsnameserver file will only hold IP addresses of available MDCs.
If you are more into config files, just delete the IPs of any missing MDCs in /Library/Filesystems/Xsan/config/fsnameservers.
Whatever you choose to do, afterwards your Xsan volumes will activate and can be mounted on your clients again.
As a simple rule you can remember, that after a complete system shutdown you need to make sure that all of your MDCs need to be turned on first before you activate your volumes. I consider this a security feature, as Xsan volumes are meant to be highly available, and to make sure this is the case, you need all of your MDCs up and running.
A second rule should be not to mount your Xsan volumes on your MDCs. I experienced, that my Xsan crashed from time to time, when I rebooted a MDC with an Xsan volume mounted. If you need to mount an Xsan volume on your active controller to configure affinities, don’t forget to unmount the volume after your work is done.
UPDATE: In fact, Apple has always recommended to boot up all of your MDCs first before you start an Xsan volume: http://docs.info.apple.com/article.html?artnum=301787.
Yet, until Xsan 1.3 you were still able to start your volumes with only one of multiple MDCs booted up.