Dynamic disks are a contentious practice among Windows administrators. IT pro Rick Vanover explains where new features and old practices collide.
When Windows made dynamic disks available, administrators were given an incredible amount of functionality to handle the problem of storage growth. Windows Server 2008 (and late editions of Windows Server 2003) offer additional features to manage storage now with the ability to easily expand and shrink disks. So if it's easy to expand a basic disk in the Disk Management snap-in, are dynamic disks still relevant?
In my opinion, dynamic disks are not quite ready for the IT graveyard. This is due to storage products usually gravitating around the 2 TB limit for single addressable logical unit numbers (LUNs). Some storage processors in storage area network (SAN) products limit LUN sizes to 2 TB for broad compatibility for server operating systems utilizing block storage (fibre channel or iSCSI). Network attached storage (NAS) offer a file-based namespace and frequently can utilize a larger size than the 2 TB limit. In my Windows practice, I occasionally exceed the 2 TB limit, and I learned a bit along the way in my recent post on NTFS allocation unit sizes for large volumes.
While I am very happy with Windows Server 2008 and its new features, I still have a use case for dynamic disks. Basically, once the storage requirement exceeds 2 TB, the use case for a dynamic disk becomes an option. Ironically, I don't find much help in terms of virtualization. For VMware environments, the VMDK disk format is limited to 2 TB for each file. A raw device mapping (RDM) can be utilized, but the VMware side of me wants to nudge virtual machine storage provisioning toward the VMDK disk format. Microsoft can do a little better here with Hyper-V with NTFS's size scaling, which works a little better than VMFS in terms of Terabytes.
I am, however, very clear about stating that I'm not in favor of using Windows' mirroring or RAID 5 features -- you can always do this better on the SAN.
Where are you with dynamic disks in your server administration practice? Share your comments in the discussion.
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