2012-05-24 06:01 PM
You didn't specify what stream you want to study so I am going to assume you're interested in Data ONTAP 8.0 7-mode administration. I recommend the Data ONTAP 8.0 7-mode NCDA NSO-154 Certification Study Guide in conjunction with the Data ONTAP product documentation.
The exam seems to put a lot of emphasis on block storage (particularly FCP) and SnapVault so make sure you are confident in these areas. There are a lot of questions that require exact knowledge of ONTAP command line syntax.