A question recently came in on the bloghotline from a customer who asked about implementing scalable storage on server clusters and how to avoid downtime when storage needs to be extended. One of our cluster PMs, Elden Christensen, replied as follows:
. . . . . . . . . . . . . . . . . .
In regards to the ability to dynamically increase volume sizes to eliminate downtime, this can be accomplished today on Windows Server 2003 with basic volumes using the DiskPart utility. After dynamically extending the LUN size in the storage cabinet, you can use this utility to extend the volume size. See the DiskPart Help on the web for the DiskPart syntax. Diskpart is available as a download utility for Windows 2000 and is included in the product in Windows Server 2003.
You can also use Diskpart on Failover Cluster volumes to dynamically extend volumes with no down time. Here's a KB that discusses how to use Diskpart on clusters: 304736 How to extend the partition of a cluster shared disk .
You can also use dynamic disks to create spanned volumes, where a volume can be dynamically extended to all another separate physical LUN, and extend the single logical volume over multiple LUN's.
Note that dynamic disks are not natively provided in the core Windows Server operating system for failover clustering. Support can be added by purchasing the Storage Foundations product by Symantec. Here is a KB article with details: 237853 Dynamic Disk Configuration Unavailable for Server Cluster Disk Resources .
An important distinction between Dynamic Disks and DiskPart is that Diskpart can be used to extend a partition on an already existing LUN where the size of the existing LUN has been increased. Diskpart is not used to span a volume over multiple disks/LUN's.
Another option is that additional storage capacity can be added and preserve the single name space for users by using volume mount points (also called mounted drives). With mount points, volumes are mounted under directories, such as D:MarketingPresentations. Users access Marketing as they are used to, but the Presentations directory can actually reside on a separate volume/disk. This allows you to increase storage capacity without impact to users.
You can also create volume mount points on clusters, here's an article that discusses how to do that: 280297 How to configure Volume Mount Points on a clustered server .
I have outlined several ways that you can dynamically increase storage capacity on the fly with no down time today with Windows. I hope you find this helpful.
--Elden
