I just got this question from a blog reader:

We have a SQL 2005 cluster active/passive.   Under my understanding, it would be neccesary to apply patches into a Testing environment, if working fine, proceed to the production environment... but, is it recommended to patch both nodes the same day?  or instead it would be better to patch Node1 (active) and wait some days before patching Node2 (passive)?

I would like to know your opinion on this matter !

Thanks a lot for your support.

The answer is you always must patch all nodes at once using SQL 2005.  Rolling upgrades/patches was introduced in SQL 2008  The patch process for SQL 2005 and lower is disruptive in that it takes the entire instance offline on all nodes to apply binary and internal patches.  Very risky and a major reason you test this on a practice cluster first.  When you apply the patch to the test cluster, you are not only testing the patch itself, but your procedures for applying and removing it if necessary.

Hope this helps.