May be considering DAG, but I have a few questions.

I kicked around a bunch of scenarios a couple weeks ago with you guys, but didn't think I had the budget to consider DAG.  Now 2 weeks before starting a pilot I seem to have some cash.  Brief history: I have about 300 users.  I have a main office with 260 and two satellite offices with about 20 users.  All offices are connected with T1s back to the Home Office.  The satellite offices will get 2 servers 1 to do DC, GC and host a bit of data and 1 to host exchange(I know it's overkill, but they hope to grow.)  The main office right now has 3 servers that can be dedicated to Exchange.  They are dual 6 core boxes with 36Gb of RAM and 1.2Tb HD RAID10w/hot spare.  I initally thought of mimicking my Groupwise system which which would mean one server each for Sales, Engineering and everyone else.  All with CAS, MBX and HUB roles installed.  It looks like Exchange doesn't necessarily use single instance storage and routes everything through HUB servers so I guess there is little benefit to this. 

So, I have been looking into DAG / HA solutions a bit more.  Now the questions...sorry if they are basic but you can find more detail oriented info on this easier than big picture on the web.

1. I understand the 2 server DAG would effectively mirror 1 server to another but would a 3rd server just create an additional mirror or will it add space(sort of raid 1 vs. raid 5)?

2. What if I find my users filling up the system quicker than a year(we intend to archive everything older than a year with an external product like Enterprise Vault)?  Would I add two servers and do another DAG?

3. If I do a DAG, should I put MBX roles on the two servers in the DAG and the CAS/HUB roles on my left over server?(Obviously I will tone down the HD space on server 3 and use it elsewhere)

4. Will one server to do the HUB/CAS be sufficient?  I have the intention of looking into the F5 product but that would be down the road.

 

Thanks for your help.  Pending favorable replies, my system is looking to be quite robust!

Source: http://social.technet.microsoft.com/Forums/en-US/exchangesvrdeploy/thread/b115ac40-5e85-4cc6-a35f-ab44b8d8c711

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