File system Alignment – All the kids are doing it

Ever since I was a boy, or, at least, ever since I started working with CLARiiON arrays (when R11 was, er, popular), I’ve been aware of the need to align file systems that lived on the array. I didn’t come to this conclusion myself, but instead found it written in some performance-focused whitepapers on Powerlink. I used to use diskpar.exe with Windows 2000, and fdisk for linux hosts. As time moved on Microsoft introduced diskpart.exe, which did a bunch of other partition things as well. So it sometimes surprises me that people still debate the issue, at least from a CLARiiON perspective. I’m not actually going to go into why you should do it, but I am going to include a number of links that I think are useful when it comes to this issue.

It pains me to say this, but Microsoft have probably the best, publicly available article on the issue here. The succinctly titled “Disk performance may be slower than expected when you use multiple disks in Windows Server 2003, in Windows XP, and in Windows 2000” is a pretty thorough examination of why or why not you’ll see dodgy performance from that expensive array you just bought.

Of course, it doesn’t mean that the average CLARiiON owner gets any less cranky with the situation. I can only assume that the sales guy has given them such a great spiel about how awesome their new array is that they couldn’t possibly need to do anything further to improve its performance. If you have access to the EMC Community forums, have a look at this and this

If you have access to Powerlink you should really read the latest performance whitepaper relating to FLARE 29. It has a bunch of great stuff in it that goes well beyond file system alignment. And if you have access to the knowledge base, look for emc143897 – Do disk partitions created by Windows 2003 64-bit servers require file system alignment? – Hells yes they do.

emc151782 – Navisphere Analyzer reports disk crossings even after aligning disk partitions using the DISKPAR tool. – Disk crossings are bad. Stripe crossings are not.

emc135197 – How to align the file system on an ESX volume presented to a Windows Virtual Machine (VM). Basic stuff, but important to know if you’ve not had to do it before.

Finally, Duncan Epping’s post on VM disk alignment has some great information, in an easy to understand diagram. I also recommend you look at the comments section, because that’s where the fun starts.

Kids, if someone says that file system alignment isn’t important, punch them in the face. In a Windows environment, get used to using diskpart.exe. In an ESX environment, create your VMFS using the vSphere client, and then make sure you’re aligning the file systems of the guests as well. Next week I’ll try and get some information together about why stripe crossings on a CLARiiON aren’t the end of the world, but disk crossings are the first sign of the apocalypse. That is all.