NetApp mbrscan and mbralign for Virtual Machine Alignment In-Depth

Alignment of VMware virtual machines has been an issue for quite some time. This issue exists no matter who is the storage vendor is but I will use NetApp because it is what I know. Here are some links to get you up to speed in case you don't fully understand the situation:

Link to VMWare document on alignment
Link to NetApp document on alignment

What has NetApp done about the situation? I hear that NetApp will be releasing a tool that plugs into vCenter specifically for vSphere 4.0 and vSpherei (ESXi) 4.0 shortly. In the meantime, if you are still on ESX 3.5 (or vSphere with a Service Console) there is another answer that you can use today. This will not work on ESXi since you need a service console for the tools.

Eric Forgette at NetApp created a set of tools about a year ago that has matured and found its way into the NetApp VMware Host Utilities Kit version 5.1. If you do not have this loaded on your ESX/vSphere servers and you are connecting to NetApp, go load it NOW! (A reboot is required for the settings to take affect) Most of the following is research I have conducted in conjunction with conversations directly with Eric over at this thread on NetApp Communities.

Included in this tool are two executables, mbrscan (scans a vmdk for alignment) and mbralign (performs the alignment). The default installation location is /opt/netapp/santools.

While the readme does a good job of going over the basics, there are a number of caveats to run the tools correctly. I will go into each executable in depth but before I go down into the weeds, you need to know when NOT to run it!

You can not or do not want to use the alignment tool for the following:

• Windows 2008 Server is aligned if the machine was created as a Windows 2008 server. If the machine is upgraded from Windows Server 20003, it will not be aligned.
• Citrix Servers are not supported because they remap the c:\
• Windows Dynamic Disks are not supported and will be corrupted if an alignment is performed (but mbrscan will detect them - see below)
  
• Linux LVM volumes are not supported (mbrscan may NOT detect all LVM partitions)
• Windows Server 2003 non-boot disks that have been added (d:, e:, etc) will need to be remapped in Computer Management. The drive letter will be lost on alignment.
• GRUB booted Linux and Solaris will need to have GRUB reinstalled after alignment

With all that out of the way, it is a basic two step process: 1. run mbrscan, 2. run mbralign on machines as needed.

Step #1 - mbrscan

• In order for the mbrscan to give reliable results, the machine must either be powered off or have a VMware snapshot!
• I have a simple script that I put together that just takes a VMware snapshot on all machines on an ESX/vSphere host.
• I then execute mbrscan using the scan all virtual machines parameter: mbrscan --all
• After I have the scan results I need I execute another script to remove the VMware snapshots I just created for all machines on the host
• NOTE: Windows Dynamic Disks will report a partition type of: unknown - 0x42. Do Not Align These Partitions!

Step #2 - mbralign

• In order to perform an alignment, ALL VMware snapshots MUST be removed!
• In order to perform the alignment, you NEED an amount of free space equal to the size of the vmdk. mbralign will make a backup of the file as the first step. This file have an extension: -mbralign-backup.
• In order to perform the alignment, the virtual machine MUST be powered off!
• If the virtual machine has multiple vmdk's, only one can be aligned at a time! 
  
• Execute mbralign against the vmdk - I usually get about 1-2GB per minute speed
  
• Boot up the virtual machine. If it works, delete the -mbralign-backup file
• On Windows systems it will ask you to reboot one more time because it detects the hard disks as new hard disks
  
• If it doesn't work, run mbralign again and it will detect the -mbralign-backup and ask you if you would like to restore the file. Very Nice!