VM /ETC

It’s inevitable. If you are a virtual infrastructure administrator, architect, or blogger you will eventually talk about VMware VMFS and virtual disk alignment. I’m not going to try to explain the concepts in this post. My goal is to discuss whether to align VMware virtual disks (VMDKs) and what options are available for performing the alignment.

Bottom line is that if you are deploying new VMs from a template you should do so from an aligned master, but VMs created from physical to virtual migrations (P2Vs) present some practical challenges and don’t have to be treated as urgently.

Recommendations

First things first. My interpretation of VMware’s stance on alignment is that they do not advocate aligning every P2V-ed VM to the VMFS due to the administrative effort, disk space requirements, potential VM down time, and in most cases a nominal VM performance increase. On the other hand, it is crystal clear that VMware does recommend always formatting VMFS LUNs with the VI Client and always taking the time to align Gold Image templates so new servers deployed will automatically be aligned.

For reference here’s VMware’s PDF on the topic:

I’ll admit my perspective as a consultant may be a bit different than the normal VI admin. After all, I am mostly involved in the

planning, implementation and migration phases of VMware infrastructure, and I am always limited by the time budgeted to perform a statement of work. Personally, I make it a point to discuss the benefits of alignment in detail with clients (often aided by my storage engineers), but then have to move on after demonstrating alignment only on the gold image template. This leaves the decision to schedule VMDK alignment up to the client during routine outage windows or possibly multiple outages if they have a large environment.

All that being said, understand that the storage device benefits tremendously from the VMFS and VMDK alignment. Especially storage devices that provide other application data to servers outside of the virtual infrastructure. An example would be a non virtualized Exchange or SQL server with FC or ISCSI volumes. Obviously, your VI benefits as well from a storage device that doesn’t have to work as hard.

Options

There are 3 options for accomplishing VMDK alignment that I am aware of.

• Manually with diskpart or fdisk before adding data.
• NetApp’s ESX Host Utilities – mbrscan and mbralign
• Vizioncore’s vOptimizer Pro

Some brief information about these tools and methods:

Diskpart or fdisk

• Must run from a command prompt on a VMDK before formatting and any data
• Do not run for boot partitions
• Step by step process explained in VMware .pdf linked above

NetApp Host Utilities

• Requires NetApp NOW account to download
• Requires VM downtime
• Requires free space on the VMFS LUN equal to the size of the .vmdk + 20% (100 GB .vmdk needs an extra 100 GB for copy made during alignment) 20% is for health of ESX
• Manual script run on the ESX hosts
• does not automatically clean up after itself. If you align a 50 GB VMDK there will be a 50 GB copy of the VMDK that needs to be manually removed after completion
• multiple disk VMs need to have alignment on each VMDK performed separately

I seem to remember reading a blog post or Twitter conversation where it was discussed that the NetApp mbrscan and mbralign tools work for VMs on any vendor’s storage but I could not find a link. I’ve personally never done it, and I question a decision to use these tools in non NetApp environment – especially production. I am eagerly awaiting version 6 of the Host Utilities that will be installed as a plugin to vCenter.

NetApp also has a PDF about alignment.

Vizioncore vOptimizer Pro

• Requires VM downtime
• Automated process that can be scheduled
• Can scan VMs first to determine tool’s total impact
• For windows VMs only, but does more than alignment – storage reclamation and guest optimization See user guide for more info.
• Requires VM Tools to be installed
• Requires VMs have network connectivity to vOptimizer server
• vOptiizer Pro server can be a VM
• Doesn’t work with RDMs, open ESX snapshots, or thin provisioned VMs
• Storage vendor agnostic
• Only works with ESX 3.0.1 or later and cannot be used with ESXi

There is a vOptimizer Pro demo that provides a great visual of all the features, and you can get a trial version that allows for 2 VM optimizations.

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