I am building an Exchange 2010 environment and am trying to determine the amount of storage that will be required for the 2 Mailbox servers. Here are the specs:

  • 2000 user mailboxes (per mailbox)

  • 2gb storage per mailbox

  • 2 physical mailbox servers in DAG

There will be copies of the other server databases on the mailboxes for failover, so even if say each mailbox has a "healthy" copy of the other mailbox's db that still comes to 8+ terabytes with my math (2000 x 2gb = 4000gb ...+4000bg copy from other server) Now of course the OS, Exchange, Log files..etc will take up space, but Microsoft's calculator after plugging into came up with this:

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16+ terabytes seems a bit high! Please correct me if I am wrong. How much storage is actually necessary per 2000 user server?

4 Answers 4


That also looks about right to me. Do keep in mind that you won't be using all of that at once, so plan for expansion. You can start smaller, but so long as you can add space when you need it you can grow into that size.

Another thing Microsoft recommends is to keep your individual database sizes down. Should any one of them blow up, a 1.9TB DB is going to take days to run ESEUTIL on should that be required, and that'll be days without email for those users. We recently split our own 4400ish user environment from 2 Mailbox servers and 7 databases to 4 Mailbox servers and 16 databases, in large part because of this.

  • +1 MS Recommends ~50 users per database for the average installation.
    – Chris S
    Commented Sep 16, 2010 at 17:41

If I am reading your numbers correctly, and you said 2000 users per mailbox server, then the math looks good to me. (4GB mailbox store + 4GB copy from other server) * 2 servers = 16TB. Of course Exchange isn't my thing, so I can't really comment on if the copy is really that big or not.

  • 1
    Did you mean 4TB
    – Zoredache
    Commented Sep 16, 2010 at 16:28
  • Now I am just questioning what will be the best but still affordable way to store the data and be redundant..
    – Chase
    Commented Sep 16, 2010 at 16:32
  • I don't think there is a way to store that volume of data redundantly, and be affordable.
    – DanBig
    Commented Sep 16, 2010 at 16:41
  • Yep, sounds right to me. I'd consider running more than 2 servers, 1000 4GB users per server sounds a bit high, but it depends on your environment. All you need is ~10 1TB drives in each server (for RAID5). Brand new servers like that will run you less than $10/user.
    – Chris S
    Commented Sep 16, 2010 at 16:43

Edited as I reread the question:

If you're doing 2000 mailboxes per server in a single database per server:
2000 mailboxes * 2GB = 4TB per database

If you have 2 active databases: 4TB * 2 databases = 8TB for active databases

but you have two servers in a DAG so each server requires 8TB:
8TB per server * 2 servers = 16TB total storage

The chart you threw up there as 16+TB total storage for the whole environment (meaning both servers) which fits.

  • That *does make sense, I thought that the required disk space was being determined for each server.. not total disk space which would make sense if you were using some sort of storage array. Thanks
    – Chase
    Commented Sep 16, 2010 at 18:20

I concur with TerryS, the maths look good. From experience I would warn you, though. Don't expect this to work too well. 2000 mailboxes per server is definitely on the very high side of things.

I would suggest you have a chat with some experts on MS Exchange. Most likely they will tell you that you shouldn't have more than a few hundred mailboxes per server. And most likely you will want some CAS servers in front of the servers holding the mailboxes, so that the users don't notice when one of them is undergoing maintenance.

  • I don't think that 2000 mailboxes on a server is that high - we have 3000 on one server and it performs fantastically well. The pressure points for performance and "how many users" tend to be how much space per user (2Gb is high, fair enough) and more importantly how many of those users will be accessing their mailboxes at the same time (about 50% for us).
    – Rob Moir
    Commented Sep 16, 2010 at 18:04
  • Well, maybe I am a burned child. Our top brass don't want any limits on mailboxes, so some users have up to 20GB in their boxes. And all of our users are pretty much connected all the time. Plus: most of them are Linux users, so they connect via IMAP, which puts extra strain on the server.
    – wolfgangsz
    Commented Sep 16, 2010 at 20:14

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