We had a 3-drive Windows Server 2008 R2 RAID-5 fail (operating in redundancy mode):

• WDC 1 TB
• WDC 1 TB
• WDC 1 TB

We removed the failed hard drive, and put a WDC 1 TB drive (that we had standing by) into the machine.

When launched, Disk Manager, asked permission to "initialize" the disk as either:

• Master Boot Record (MBR)
• Guid Partition Table (GPT)

We initialized the disk as GPT, converted it to dynamic, and tried to use the Repair Volume command - except it was greyed out. (which is a terrifying thing on a failed production server hosting 3 virtual servers)

i tried from the diskpart command line tool. First we look for our RAID-5 volume that is in Failed Rd mode:

DISKPART> list volume

  Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
  ----------  ---  -----------  -----  ----------  -------  ---------  --------
  Volume 0     E   VMs (Raid5)  NTFS   RAID-5      1863 GB  Failed Rd
  Volume 1     D                       DVD-ROM         0 B  No Media
  Volume 2         System Rese  NTFS   Partition    100 MB  Healthy    System
  Volume 3     C                NTFS   Partition   1862 GB  Healthy    Boot

There, Volume 0. Make that our active context:

DISKPART> select volume 0

Volume 0 is the selected volume.

Now we need to find the disk we will be repairing the volume with:

DISKPART> list disk

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0    Online          931 GB      0 B   *
  Disk 1    Online          931 GB   931 GB        *
  Disk 2    Online         1863 GB      0 B
  Disk 3    Online          931 GB      0 B   *
  Disk M0   Missing            0 B      0 B   *

The disk with 931 GB free, Disk 1. Now we just need to repair the volume:

DISKPART> repair disk=1

Virtual Disk Service error:
The size of the plex member is invalid.