I had a lot of fun at Microsoft Tech Ed 2010 in New Orleans this week. One session I attended was a follow up to a Microsoft blog posting about the top 10 Exchange storage myths. Listening to the Exchange team explain the rationale behind some of the information was pretty fascinating and helped me understand just how far Exchange has come in the past few years. It also caused me to rethink some of my opinions about Exchange storage.
Myth: Exchange doesn’t support SATA disks
Exchange storage requirements have undergone a massive transformation. Storage performance needs used to be so high that Microsoft recommended only the best of the best when it came to storage solutions; with Exchange 2010, Microsoft is very much moving down the storage ladder with full support for SATA disks in Exchange 2010. This is not to say that SATA disks are bad, but rather that Microsoft seems to be working hard to make sure that Exchange is an affordable solution.
One trade-off since Exchange 2003 is that, in Exchange 2007 and Exchange 2010, Microsoft has made continuous progress in reducing storage performance need (as measured in IOPS) at the expense of capacity. This makes sense. Over the years, storage capacity has risen exponentially, while the cost for an individual disk has plummeted. At the same time, storage performance has remained relatively constant; disks still spin at a maximum of 15K RPM, and RAID hasn’t changed for a long time, either. In many cases, organizations don’t need to worry about storage capacity, even on SANs; disks are so huge now that space isn’t an issue. However, because disk performance has not kept pace with other advances, it is still a bottleneck.
In Exchange 2007, Microsoft made significant changes to the storage architecture that resulted in a massive drop in IOPS need. And, in this case, lightning has struck twice: In Exchange 2010, Microsoft made another leap in IOPS reduction by fully eliminating Exchange’s Single Instance Storage (SIS) feature. By eliminating SIS, Microsoft is able to use storage in a much more sequential way (as opposed to a random way); this is one of the primary methods by which the company has been able to achieve such impressive reductions in IOPS need. According to the Exchange storage session I attended, 70% of the overall IOPS reduction is due to Exchange’s newfound ability to run very sequentially. When you start to calculate storage vs. IOPS costs, especially as disk sizes have increased so much, it’s easy to see why Microsoft has been steadily moving in the IOPS reduction direction.
So when you’re sizing your Exchange 2010 infrastructure, you can think more about capacity than storage performance. Want to use low cost SATA disks? Go ahead. It’s still important that that the storage architecture keeps up, but no longer is it the storage driver.
NAS-based storage with Exchange
In other storage not-so-news, Exchange 2010 continues to eschew the use of Network Attached Storage (NAS). Apparently, some enterprising individuals have gone to great pains to attempt to expose NAS-based storage as, say, iSCSI, etc. to Exchange servers. I say this because Microsoft went out of its way to stress that NAS, regardless of how it’s presented to Exchange, is not supported for Exchange and that its guidance would be updated to clarify this fact.
In order to clarify the use of iSCSI, sometimes confused with NAS, someone in the audience asked if that meant that iSCSI would no longer be supported under Exchange 2010. It’s important to understand that iSCSI-based arrays are not NAS in the traditional sense of the word; iSCSI provides real block-level storage services that are fully supported by Exchange.
Don’t try to use NAS-based storage with Exchange. Get a block-level array and try again or simply moved to direct-attached storage.
I’ve read quite a few complaints about Microsoft’s move away from SIS and the potential increase in storage need from a capacity perspective, particularly as organizations implement Exchange 2010’s Database Availability Groups (DAG) feature. It’s important to note that a GB is cheaper than an IOP in most cases, especially if you can use Exchange on SATA disks.