Tuesday, January 4, 2011

Partition Alignment with ESX and Windows 2003. Just do it.

You really want to make sure your partitions are aligned.

Partition Alignment, in a nutshell, is making sure your partitions start on Sector # 2048 (or some multiple of 512) instead of the standard Sector # 63.

There are some great blog entries that define the issue, so I won't get into it here.

While you don't need to do this for 2008 partitions (they start properly aligned), I've always known I should align my older 2003 partitions, but I haven't bothered. Today I decided to do a simple test to see the results of running un-aligned.

Test Details:
OS: Windows 2003 32bit
Test Package: Performance Test 6.1, running Webserver disk role benchmark
VM: ESXi 4.1
Drives: NFS share to a Solaris 11 ZFS box.

I chose the webserver role because it's a heavy reader (writes are harder to benchmark on ZFS), and because it's my worst performer. The other roles are hitting 900-1200 MB/sec, which is close to the max I can drive through my 10Gbe card. 

Aligned Partition: 609 MB/sec
Non-Aligned Partition: 436 MB/sec

That's a 30% increase in read speed. Wow, that's a lot of speed to throw away for not aligning a partition. 

Here's a link to a quick little tool that will let you know within Windows if your partition is aligned: http://ctxadmtools.musumeci.com.ar/VMCheckAlign/VMCheckAlignment10.html

Of course, it can be a pain in the ass to align a partition. You can use a livecd of gparted, or create a new disk and partition it with Windows 2008, copying the data to the new partition from a seperate VM.

Some partition tools are now including the ability to quickly and easily specify a aligned-partition start, so hopefully this will be an easy task in the near future.  If you know the name of any easy booting GUI type partition tools that can move a Windows partition to sector 2048 without much fuss, please let me know and I'll post it here.

I personally do it with gparted live, but I'm also not affraid of the command line. Something easier would be nice.


  1. Found this post and thought EUREKA!

    Confirms my suspected problems in ESXi, point to the software that helps identify the alignment problem and then tells me the tool to use to fix it.

    But - I must be having an off day as there is no way I can gparted to run - go into resize and change the alignment - it fails with an unknown error that no other disk software can find - I am certain I have missed something very obvious but any chance of giving me a clue



  2. Hmm, try a different packaging of gparted - I'm having good luck with the Parted Magic ISO distribution.

    You can also try the Paragon Partition Alignment tool - It's quite cheap ($29 I believe) and runs as a Windows GUI wizard.

  3. Thanks for the suggestion - also received some advice that I need to move the partition well above the 2048 sector/ 1MB point and then move it back to the 1MB point.

    Trying again to-night!