Is Windows 2008 the End of Dynamic Disks?
There's a saying, "What you can do and what you should do are two different things." This saying rings true for many virtual environments – in my travels supporting customers, I've seen some strange system configurations.
Using dynamic disks with Windows 2008 is a great example – and a common one – of what you can do and what you should do being two different things. Dynamic disks have had a proper place in virtual environments. However with the changes Microsoft made starting with Windows 2008, and with vSphere's ability to hot expand VMs, dynamic disks may not have a place in virtual environments any more.
Dynamic disks started with Windows 2003 and have been a good way to expand storage. However, dynamic disks were not always configured or used in the most beneficial way. The storage where your VMDKs or virtual disks reside should be in a RAID configuration, not in the virtualized OS. Yet I've seen up to 11 VMDKs attached to a single VM in a RAID 0 configuration. A Windows 2003 basic disk does not allow storage to be managed without powering down the VMs. The inability to manage storage hot forces users to find other, more creative ways to manage storage.
Starting with Windows 2008, Microsoft made updates that may make dynamic disks unnecessary. With Windows 2008, Microsoft greatly enhanced the functionality of basic disks, including support for hot storage management and the ability to use basic disks for GPT partitions.
vSphere now supports hot expansion of VM disks, which together with Windows 2008's ability to hot expand basic disk and use them for GPT partitions, enables administrators to take full advantage of online storage management.
What's Right for Today?
If you are running multiple operating systems on a single virtual host, it is in your best interest to set up some sort of hardware RAID configuration where your VMFS will reside.
It looks to me that Microsoft is encouraging dynamic disks only for software RAID when the disk subsystem does not support a hardware RAID level. If a basic disk can be hot expanded and can be a GPT partition, it seems like the only reason left for using dynamic disk is for disk subsystems that don't support RAID configurations. Since Windows 2008 supports hot expansion and the use of basic disks for GPT partitions, I question whether you need dynamic disks if you're running Windows 2008.
Posted by Jason Mattox on 06/22/2010 at 12:49 PM