Does Exchange 2007 ask for too much RAM?

Ed Brill is making hay with Microsoft’s system recommendations for Exchange 2007 beta 2. (Don’t miss the comments, especially the ones pointing out that IBM doesn’t even publish per-user resource guidelines for their own products– good thing, because if they did Workplace wouldn’t look too spiffy!)

Anyway, Ed’s article misses the point: the recommendations are for servers with “many users with large, frequently used mailboxes”. If you don’t have many users, or they don’t have very large (>1GB) mailboxes, or the mailboxes aren’t frequently accessed, you can get by with much less RAM.

Remember, the point of adding RAM is to reduce the number of I/O operations per second (IOPS) that you need to handle a given user load. Large mailboxes and frequent accesses mean more IOPS. More IOPS means more disk spindles, which means lots more money. Gigabytes of RAM are cheap compared to SAN disks; right now, Exchange 2003 servers scale out by adding more spindles to get more IOPS. With Exchange 2007, you have a choice: add IOPS by adding disks or reduce the number of required IOPS for the same user load by adding RAM for caching. You get to choose according to your needs– part of Microsoft’s promise to provide more administrator choice and control in Exchange 2007. (Take a look at this post for more detail on disk I/O tradeoffs in Exchange 2007.)

Ed’s pricing example is a little disingenuous too, because he doesn’t specify how many Notes users his hypothetical 6200-user Dell configuration could host, and he ignores storage costs altogether. I’ll be happy to put together a reasonable configuration for N Exchange users and cost it out if you’ll do the same for Domino. (I’ve made this offer before, and Ed’s ignored it– wonder why?)

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6 Comments

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6 responses to “Does Exchange 2007 ask for too much RAM?

  1. >the recommendations are for servers with “many users with large, frequently used mailboxes”.
    Where does it say this on Microsoft’s website, Paul? You wrote it in quotes, so you must be quoting from somewhere.
    Yeah, and my pricing example is way off — because there’s no real disk storage in that $70,000 machine.
    Make the direct comparison? Well, as long as you’ll include all the products needed for the comparison, sure. If we are just comparing mail workloads, Domino’s going to come out as good or better than Exchange…but the commodity mail products are going to kick both Domino and Exchange.

  2. I quoted that from the “Note” section of the system recommendations, which originally came from MS’ website– you included that as the last sentence of the second block quote in your original post.
    Given that you’d have to buy disk storage for Domino *or* Exchange, I think it’s fair to factor storage costs into the comparison. If you wanted to have, say, 300GB of mail data– not an unreasonable amount– you’d actually need less disk for Exchange (but then we’ve been over that already).
    As for feature comparisons: you originally brought up Exchange scalability, so I was talking only about Exchange. Dragging in commodity products like el-cheap-o “good enough” [sic] Linux messaging doesn’t help make either of our cases.

  3. I haven’t ever seen a study that shows that Exchange needs less disk than Domino. When we do Exchange to Domino migrations, we don’t find that there’s any real difference in the disk space utilized in those deployments, especially not when measured across all servers.
    You define “large” as a >1GB mailbox — is that MS’s position? From what I’ve read/seen, it’s not like there is that much experience with Exchange mailboxes in that size range today.

  4. You & I both know that single-instancing works to conserve disk space. You can dispute (and have!) the tradeoff between having a large number of individual files for individual mailboxes or a smaller number or larger databases, but I think you’d probably agree that given two equal sets of mail, using a single-instanced database would be a more efficient use of disk.
    The real question isn’t disk storage, though, but performance. Microsoft publishes clear guidelines on disk I/O scaling for Exchange. I’d love to compare them to IBM’s recommendations for Domino, but I can’t seem to find any.
    As for what “large” means, that’s my definition, not Microsoft’s. In my experience with customers, less than 10% of customers have mailboxes larger than 1GB (or, more precisely, 10% of individual mailboxes over that size). Most of the sites that do have larger mailboxes wish they could get rid of them, too, but that’s a separate conversation.

  5. Might want to take a look at Jack Dausman’s posting on Exchange vs. Domino disk space… this is typical of what I’ve seen and why I made the assertion in the previous comment.
    http://www.leadershipbynumbers.com/MS.nsf/d6plinks/JDAN-6SNSH2

  6. Thanks, Ed– I read Jack’s posting and responded with my own comments at http://www.robichaux.net/blog/2006/08/exchange_storage_and_compaction.php.