Fantastic post on disk alignment and VMs
If you haven’t heard about disk alignment and you’re using virtual machines, you owe it to yourself and your most-likely-growing infrastructure to understand what alignment is all about. On a small scale it’s almost unnoticeable. But I can tell you that on a large scale it becomes a major pain for you or your storage infrastructure team.
One quick tip: to check your disk offset on Windows systems, simply launch msinfo32.exe from the Run menu. See the thumbnail of this post for a screenshot.
From VirtualGeek’s excellent post:
The purpose of alignment is to minimize extraneous internal array operations. All arrays have internal constructs that are generally a function of the RAID model (and also the filesystem alignment, and in some cases logical page table constructs in virtually provisioned models).
<snip>
All the funky goodness is done via either filesystem or another (pages commonly) abstraction on TOP of the RAID abstraction. Think of a 4K NTFS IO operation in a Guest making it’s way down to the array. Once it gets there, let’s say the array has a 64K stripe, but a 1MB “page” used for these fancy features. Falling into two 1MB logical memory pages as an example – where statistically it’s much more likely to land on a boundary if the volume is aligned on a 4K boundary.
It’s very worth your time to delve into this article and find out how your environment is set up, like right now. You might find your templates are mis-aligned, or in our case, that VMware Converter does not properly align disks on conversion (wonder-app Platespin Migrate does, in fact, give you properly-aligned disks).
Categorised as: Virtualization