If you are in s situation where you need to expand a disk and you happen to have either a DAS array or a SAN backend you can dynamically grow, you can then extend the existing volume to "grow" into the space you just added. Please note you are limited though by a few things:

• If this is a basic disk, the new space HAS to be the next contiguous block else it wont work
• If this is a dynamic volume, you can extend with no restrictions on where the space is so long as its the "same" disk
• You can't extend the primary OS partition in this fashion
• You can only "grow" space and not "shrink" it... So be careful what you do when you do this
• This operation can be done ONLINE but its not typically recommended for an SLA environment. Be sure you have a good backup just in case things go wrong.
• Although not recommended, you can do this operation on a cluster disk ONLINE as well if needed

So, now that you have decided to do this you can then perform the following steps:

1. Login via RDP into the system in question and open up a command prompt
2. Type "diskpart" and press Enter
3. Type 'rescan' and press enter (without a rescan the new disk will be unavailable)
4. Select your disk that you want to grow the space on
   • If you are unsure of the disk number do a list disk
   • Command for this is:
     

     select disk X (where X is your disk number)

5. Next select the volume you want to grow
   • If you are unsure of the volume number do a list volume
   • Command for this is:
     

     select volume X (where X is your volume number)

6. Finally, to grow the volume enter the following command:
   

   extend size=XXX (where XXX is the size you want to grow the volume in MB)

7. To check, open up the Computer Management MMC and go under Disk Management to confirm the disk was grown to the appropriate size

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For more information, please feel free to reference the Microsoft knowledge base document below:
http://support.microsoft.com/kb/325590