Exchange 2010 Mailbox VM I/O Sizes

Exchange 2010 Mailbox VM I/O Sizes

One of the big areas of improvement with Exchange 2010 was with how it handled I/O. Specifically the individual I/Os are now bigger. In my blog post on VROOM! about Exchange I/O performance, I looked at how adding more RAM decreases IOPS and improves performance. But it didn't look specifically at the size of the I/Os - which is what this blog is about.

Using the vscsistats tool that comes with ESX it is possible to get snapshots of storage performance. One of the things that it show is the size of the I/Os for the interval sampled. This size info is detailed down to individual virtual disks for individual VMs. This makes it possible to see the size of reads and writes for the data and log disks on our Exchange 2010 Mailbox Server VM.

I sampled vscsistats data while running LoadGen 2010 beta with an 8000 user Outlook Online 2007 Heavy Profile across four Exchange 2010 Mailbox server VMs (Gabe has a good summary of how to use vscsistats). I collected the data against all four Mailbox VMs, and the data was essentially the same, so I'm just reporting for one VM. This data is based on an approximately 5 minute time period for 2000 users on a single Exchange 2010 Mailbox server VM. The chart below shows the number I/Os for each size, but also denoted by color for data disk reads, data disk writes, log disk reads, and log disk writes.!http://communities.vmware.com/servlet/JiveServlet/downloadImage/9684/vscsistats_IOsizegraph.JPG!

I/O operations on the data disk were all 32K or higher, with a large majority of them at 32K. I/O operations to the log disk were of a completely different profile with exclusively writes and the vast majority of them being less than 32K. This shows that Microsoft Exchange 2010 does not use the smaller 8K and 4K I/Os for the database as in previous versions.

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