Eswar -
Welcome to the NetApp community !
The NetApp exams are not easy to pass, even for a seasoned NetApp instructor.
I teach the NCDA, ANCDA, and ANCDA87 boot camps for NetApp University. Taking one of these courses is an excellent start to preparing for the 154 exam, or the 153/163 exams to earn your NCDA certification.
One of the things I tell my students on the first day of these boot camps is that they need to study, not just expect that the lecture and labs will get them through these exams.
The primary references to study are the various guides that comprise the Data ONTAP documentation for any given release. In my younger days I'd say 'Just give me the man pages, and I'll figure it out !'. This was a mistake on my part. Documentation is available on the NOW.netapp.com site, or may be loaded up already on your NetApp. You can order hard printed copies for no charge from the NOW site. For the NSO154 you would want to pay attention to the DOT8/7-mode release notes.
In addition to doing the study work, you would probably want to set up a lab environment to practice using Data ONTAP. There is a NetApp simulator available for download from the toolchest section of the NOW site. You can run the simulator on a LInux host system. Unlike other simulators I've used over the years (like Cisco IOS sims) the NetApp simulator isn't just a program that will mimick the command line, it is a running copy of Data ONTAP. The only things simulated are the disk drives (simulator files) and network interfaces (promiscuous mode on host interface). The simulator runs like a real NetApp !
When you think you're ready to take the exams, you may wish to try testing your NetApp knowledge with practice exams first. There's a set aailable on the NetApp University web site.
I'll hope this information has been useful to you. Best wishes towards your goal of NCDA certification !
At your service,
Eugene Kashpureff