x64 DCs are slowing getting rolled out to various companies. Most often I am hearing amazing things from an LDAP query standpoint which is great.
I am curious though how people are determining how many DCs they need? Are they just replacing their x86 DCs and leaving it at that or are they carefully watching performance and scaling DCs down as needed or just going forward with ball park guesses on what they will need for Exchange and Auth?
There is a nice whitepaper (http://www.microsoft.com/downloads/details.aspx?FamilyID=52E7C3BD-570A-475C-96E0-316DC821E3E7&displaylang=en) on the perf benefits of x64 for Domain Controllers but it has an omission for interactive auth. It has auth in general, but not interactive auth with the processing of GPOs, scripts, etc. This is important because you are talking about file ops which don’t appear to get that big speed boost you get with directory access.
Obviously this is all firmly entrenched in the world of “it depends” but sometimes you start with a greenfield deployment (say moving from some other OS to Windows) and can’t benchmark everything in a lab so where do you start? The ADSIZER hasn’t been updated since Windows 2000 because it has been killed, it was too easy to give false expectations. You could get burned by getting a result that was either under or overkill. Why? Because IT DEPENDS. You can understand why MSFT doesn’t want to give out false expectations… Generally in a greenfield deployment there are so many unknowns you have no clue what you are going to do or end up with. But it would be nice to have rough guidelines for a place to start. Most companies will not buy X hardware and then add to it as needed to get to Y where everything runs well. They want to know up front what Y is so they can understand their costs. You can’t argue with that other than by saying… it depends. With x86, it is a known beast, we have been dealing with it for some time and most consultants and support folks have seen it in real life under heavy load and have an idea of where you can ballpark. Not so with x64, we don’t have that built up “gut” level knowledge yet.
So let’s hear what you are doing with x64 and what your experiences have been…