There is no “DAS vs SAN” and Exchange 2010 Tested Solutions from EMC

It’s refreshing to see the most recent post on the Exchange team blog promoting real-world, tested Exchange 2010 configurations. EMC’s got two white papers we did with Cisco and Brocade highlighting the benefits of virtualizing Exchange for local and remote availability reasons.  I’m sure EMC’s Dustin Smith will have more to say on this soon enough.

The program was a great idea – led by Microsoft’s Rob Simpson that highlights both DAS and SAN connectivity options. In the Exchange world, we’ve seen plenty of documents and programs and marketing against anti-SAN approaches to the dismay of many very smart folks we talk to in the data center. This program was a healthy dose of accepting reality by a very logical thinker within Microsoft.

But… there is no “DAS vs SAN.”  The DAS versus SAN debate is not a technology debate and it’s not a cost debate and it’s not a Microsoft versus storage vendors debate.    It’s a control issue.

Let me explain.


There’s been a ton of articles written and TCO studies done to show TCO in both directions.

When it’s a DAS discussion, TCO slides in favor of DAS.   Big surprise.  Here’s a few reasons why these TCO models are usually wrong:

  • JBOD style DAS TCO calculations never take into account RAID protection – and I haven’t seen any large customer stop using RAID protection (mirroring or otherwise) on their crown jewels – their email systems.
  • DAS-skewed calculations also crank up the price by utilizing very old technology prices…  so maybe we should be more transparent about pricing to show that these prices are typically WAY off and don’t take into account list & street price factors.
  • Also they assume the wrong disk configurations which crank up the perceived price of a storage array – the configurations they are matching against DAS typically use thickly provisioned Fibre Channel drives – way more than you need for Exchange 2010.  Thin provisioning let’s you allocate storage capacity only as you need it and manage a simple pool of storage that has multiple Exchange databases across it.  Large capacity, lower cost/GB SATA drives often make up the bulk of EMC Exchange 2010 configs – unless you have a storage admin who just likes to put Tier 1 applications of FC as a rule (this does happen) and was not expressly told that Exchange 2010 should be put on SATA.
  • Also the server to storage connection itself is wrong.  When I’ve seen competitive TCO’s against EMC, I see FC connections, FC switches, FC cards … and heck if I were selling against EMC I’d do the same.  But EMC can offer iSCSI, and sure, you can buy a lower cost iSCSI switch (but don’t get one that’s too cheap), and you can now get away with pure software iSCSI initiators in most circumstances these days (look out for embedded TOEs in the foot notes 🙂

However – when it’s a SAN discussion, we obviously suffer from similar blinders.  We don’t always know about the competitive storage option and what special sauce ingredient they might be using to make our TCO model look invalid.   The one thing we do is try to show TCO over a few years and we don’t see much of that from DAS models (we stress operational cost savings, DAS models focus on short-term acquisition or CAPEX costs).

Since we are on the topic, the word SAN is often used wrong when companies compete against EMC – the world leader in storage hardware, software, and services.   Taken literally, DAS and SAN are only differences in connectivity.  DAS is simply direct attached storage – going straight from a server to a storage array without a switch in between.  A SAN is a storage area network, formed with server(s), switch(es), and storage array(s).   Used in this context, storage vendors like EMC love DAS and SANAlthough there are numerous benefits of having multiple servers sharing storage (for simplified management, protection, and virtualization), we can also let you connect directly from your server directly to an EMC array with your protocol and connection of choice.

While EMC does make the world’s best storage arrays – please do not think EMC =SAN and all SAN’s = expensive.  We have some amazing products in the lower end price bands that be configured “DAS Style” to lower costs.  Also, thin provisioning is regularly used on the Exchange mailbox database volumes to decrease the initial storage outlay (running numbers on this is quite easy:  5000 users at 5GB thick versus  5000 users that are thinly provisioned 500MB mailboxes.  The savings can be tremendous).


Technology debates are almost always irrelevant. It’s usually a mindset debate. What is the mindset of the decision maker in the company for their Exchange deployment?   Is the IT manager responsible for final decisions on the storage for Exchange, or does the storage manager make that call?  Or is the Exchange administrator empowered to make their own choices.  You have three different storage choices in each case:

The IT manager

wants something that has a great price/performance – something that works but with a reasonable price tag.  They like “standardized solutions.”  Virtualization integration has become big on this persons list.  And they can’t forget the big cloud in the room too –  hosted/public cloud options.

The storage manager

wants more of what they know – keep it simple and make it easy for them to manage growing volumes of storage.  Integration with other tools and virtualization is big for them too.  They are into the storage hardware and you need all their requirements met to make them happy.

The Exchange admin

will go with what they know.  After a few classes and conferences and blog posts, they learn a mantra of “go with DAS… not expensive SAN” and they may associate EMC with SAN and forget to think that EMC storage arrays can be direct connected as well…  We could make a voice-controlled storage robot that costs $10 and an Exchange admin still may not like it as long as it’s controlled by someone else and has the words EMC on it.

Our storage arrays keep getting better and better (like our storage robot like, zero-management, set-it-and-forget-it functionality in EMC’s Fully Automated Storage Tiering), but again it’s not a technology debate…

It’s all about control.

For years, putting Exchange on high-end storage arrays was almost required, to get that many FC disks in one place.  Now that Exchange 2010 is here, anyone can use lower cost SATA drives.  It doesn’t mean they have to go with a direct attached deployment model…  If the Exchange administrator is in control, they will choose the deployment model prescribed to them again and again.  It’s not their fault, it’s just what they are told and it’s all they know to recommend.  Just about anyone can ride their bicycle to work – but do they?

The same exact discussion is also taking place with regards to public or private cloud for email…. who controls it?  You or the hosting provider?  And are you comfortable with that?   Some folks are, and some aren’t, and some never will be.


In the end, I am very happy to see an alternative approach with this new program.  I’m happy that we participated in the program and drove two successful solutions from it.  And I’m happy that we offer a choice to customers – whether it’s the Exchange admin, or the storage team, or the IT manager that wants to decide to control the storage direction for Exchange… we have a wide range of price points (wait until you see what we have coming next week) and allow any connectivity type our customers want.

I’m disappointed when Exchange 2010 deployment discussions turn into a vendor vs vendor debate, and when bad TCO data is shown, and when our own reps are not aware that Exchange should be on SATA on not FC drives in most cases.

It’s tough educating a lot of people at once and it’s even tougher to change their mind.  The best thing to do as companies is to work together and let our customers tell us where to go next.

1 thought on “There is no “DAS vs SAN” and Exchange 2010 Tested Solutions from EMC

  1. Pingback: Attached To You: Exchange 2010 Storage Essays, part 3 | Devin on Earth

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