Account Permissions Needed to Integrate SSRS with SharePoint 2010 in Separated Machines

When Microsoft released SharePoint 2010 and SSRS 2008 R2, the integration process is lot smoother and easier then before. There are tons of information on-line to show you how to do it. I can easily find how to plan the environment, what kind of service accounts and permissions I need, how do I configure in different scenarios.

So, with so much information, I should be able to do it easily without too much trouble. Well, not exactly. One of the problems I have experienced in the past years with SharePoint configuration information is, a high percentage of them out there have assumed something but were not described clearly. For example, when I tried to configure MOSS 2007 to integrate with SSRS 2005, most of the articles I found at the time assumed that your environment was using Kerberos. However, we did not use Kerberos so it's hard to find out what should be done. This is no one's fault and it's almost impossible to put every possible scenarios into an articles. We just need to keep this in mind when we do our research.

The environment I was trying to work on was:
One WFE
One SSRS without database
One database server with all SharePoint databases

The service accounts I have are:
One Farm setup and admin account, which has DB Creator and Security Admin role. It does not have any other roles to the database system and it could not drop any databases.
One SSRS service account, which has no other rights in the database or farm.

The farm setup and admin account had created databases for web and service applications. When I logged on to the SSRS server using the farm admin account and started the SSRS Configuration tool, I had no problems to add SSRS service account and create web application for Report Server. I came to an error messages when I executed script to generate two databases for SSRS service. Though the databases were created but the whole process stopped and returned Insufficient Permissions errors.

I tried to add the SSRS service account with DBO role to the two newly created databases, I was not able to connect them through the SSRS configuration tool again. I got different error message said these two databases were not in the correct format.
I have followed the articles I can find regarding service account requirements and still not able to figure out why. Then I recalled that when we configured MOSS and SSRS 2005 integration, we needed farm admin account to have database System Admin role to the instance. Usually this is only assigned to the service accounts used by DBA team and not service accounts used by applications. I asked for this role in our instance and everything went through without another errors.

As far as I could recall, I haven't read an article mentioned this role or I may not do a good job when I researched it. Any way, this is my experience and if you run into errors when integrate SSRS with SharePoint 2010, give this a try.