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!

For 300 users a single server would be perfectly fine unless you want some redundancy. every mailbox server member in a DAG will use its own dedicated disc space for databases and transaction log files. You can configure those LUNS as you like (RAID1-5 or whatever), Exchange just uses them as discspace. Disc are cheap, just by more or use larger disc from start if you think users will fill them up. Is this why you consider using an archive system to move data away from Exchange? One server for HUB/CAS will work since you only have 300 users but it wil not give you redundancy, for that you need 2. lasse at humandata dot se, http://anewmessagehasarrived.blogspot.com

Thanks for the reply. I have 3 servers at my immediate disposal. Should I/Can I do a 3 server dag since that would require no witness with all roles(MBX/HUB/CAS) on all member servers or should I do a two server DAG with only the MBX roles and then use the third server I have to do the CAS/HUB roles as well as be the witness for the DAG? I assume it would be best to do the DAG from the beginning and I have 2 servers for that. If I start out with 1 server running HUB/CAS roles, can I add another down the road to do a load balancing scenario? Does it even matter if I configure the dag right now? With a 300 user install running on a DAG, is there any benefit to running multiple databases on the servers. Thanks for all your help. Depending on the response from this as well as a query I have at Blackberry, I hope to start pilot work next week. I am actually excited to get to the real deal!

Hi, With three servers you should do a two server DAG with only mailbox role on it. Then the last server should be hub/cas as you write. The reason for this is that you can't do a NLB cluster for CAS when you also have failover clustering enabled on the DAG. If you want multirole servers only you need a hardware load balancer (or virtual appliance of the same) to handle all the load balacing. /MartinExchange is a passion not just a collaboration software.

Thanks for the quick turn around. I will probably do the 2 server DAG - MBX only solution you suggest. I will start with 1 CAS/HUB and if user demand grows, I can add additional CAS/HUB servers with a balancer. Can this be added later? Along the lines of my previous item, is there any benefit to havign multiple databases on the the MBX servers rather than just 1 on each server? Also, I had a hardware question crop up today. Before I did the DAG, I was going to put in 11 300 Gb Hard drives in this configuration: 8 RAID10 to make a 1.2Tb volume 2 RAID1 to make a 300Gb volume 1 Hot Spare I was going to put the OS and Exchange Log files on the 2 Disk set and the actual Exchange Database and install on the 8 Disk Set. Is that still a good idea? I had been told to treat Exchange like a SQL server and that is how we would set SQL up. If this question should be in another forum let me know and I will move it. thanks for all the help !

Sure you can add additional cas/hub servers as you go along. having only 1 database on each server will not give you redundancy on the DB layer unless its a copy of each other. DAG alone wil not give you anything unless you create copies of databases and spread them on your mailbox servers in the DAG. lasse at humandata dot se, http://anewmessagehasarrived.blogspot.com

Hi, Yes you can add more CAS/HT servers later and create a NLB cluster and make some configuration changes so that the databases uses the CAS array for RPC server. As for the other question it looks ok to me, I know that MS says JBOD a lot these days, but I still like the RAID systems so that I can loose a disk without any problems. As for the number of databases I recommend that you size them after what kind of SLA you have for recovery. If you do need to restore an entire DB and you have all users in one DB it takes a lot of extra time and you need a lot of storage. I like to keep my databases around 100 GB tops, but it still depends on what kind of company I work for and what backup solution they have in place (or buy). /MartinExchange is a passion not just a collaboration software.

Two-Member DAG with a dedicated HT/CAS server looks very flexible For the question about storage configuration, you can refer to the article below: “Best Practices for Supported Storage Configurations” section in Understanding Storage Configuration As for the number of databases, agree with Martin. It’s up to the SLA “Ultimately, the overall design of a DAG, including the number of DAG members and the number of mailbox database copies, will depend on each organization's recovery service level agreements (SLAs) that cover various failure scenarios” -----------Refer to <Planning for High Availability and Site Resilience>Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

Now a really easy question. I have my 3 servers all running 2008R2 Enterprise edition and 2 of them have 2 NICs configured. What order do I do the install? I will put them in AD of course but after that, the documentation is a little murky. I think I should install the HUB/CAS roles to the server that will be witness and install the MBX roles to at least 1 of the DAG members. Which of the following seems right to do after that: 1. Do I then bring up exchange, create my databases( I think I will do 3 to start with) and make sure everything flows before installing MBX role and such to the second DAG member and then create the DAG? 2. Do I create my 3 databases on the first, install the MBX role on Dag member 2 and then create the DAG and only then really bring exchange live and test flow? If I get an answer soon I may be a running exchange site by the end of the day! I am really looking forward to getting off my old system if you couldn't tell. Thanks for the help!

Hi, I like to create the DAG first on both servers and make sure that flow is alright and that failover works as it should. It doesn't matter if you create one or three databases from start, but if you know it is three already I would just create them so the setup is complete. Oh, and yes you need the HUB/CAS as the first Exchange deployed that is mandatory. It is however optional when you add the second server to the DAG, I just like to confirm that all is alright before get to far along. /Martin Exchange is a passion not just a collaboration software.