VMTN: I/O Performance in vSphere, Block Sizes and Disk Alignment

Caution: Articles written for technical not grammatical accuracy, If poor grammar offends you proceed with caution ;-)

Yes folks, it rears its ugly head again…Disk Alignment… If you have not read it yet, check out the whitepaper on disk alignment from VMware.

First, chethan from VMware posted a great thread on VMTN about I/O performance in vSphere. The start of the thread talks about I/O, then leads into anice discussion about block size. A couple of weeks ago, Duncan Epping posted a very informative article about block sizes. It convinced me to use 8MB blocks in VMFS designs.

Finally, the thread kicked into a discussion about disk alignment. As you know, the VMFS partitions created using the VI Client will aoutmatically be aligned. This is why I advocate NOT putting VMFS partitioning into a kcikstart script. The whitepaper demonstrates how to create aligned patrtitions on winders and Linux guests as well. The process is highly recommended for any intensive app. But I have always questioned the need to do this for system drives (C:) on guests. To do it requires a multi step process or the use of a tool, like mbrscan and mbralign, And I have wondered if it was worth the effort. Well, Jason Boche gave me a reason why it should be done across the board. And it makes sense: “This is an example of where the value of the savings is greater than the sum of all of its parts.”

Jas also outlined a very nice process for aligning Linux VMs and fixing a common Grub issue. Thanks for the tip Jas!

I should also thank everyone else involved: Chethan, Duncan and Gabe!

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