I have been trying to get add a Mirror to my System drive in Windows Server 2012 R2 and I've been getting the error:

All Disks holding extents for a given volume must have the same sector size and the sector must be valid.

While researching this problem I found that the most likely reason is because the drives are not partitioned the same and I came across this article (KB951985) which gives step by step instructions how to setup the disks to mirror the system drive.

The problem is that it wants you to get the sizes of the EFI and MSR partitions using

diskpart.exe DISKPART>select disk 0 DISKPART>list partitions

According to the article I should see something like the following

Partition ###  Type              Size     Offset
-------------  ----------------  -------  -------
Partition 1    System             200 MB  1024 KB <- EFI PARTITION
Partition 2    Reserved           128 MB   201 MB <- MSR PARTITION
Partition 3    Primary             50 GB   329 MB

but since my drive has already been converted to Dynamic I see this. (This shouldn't be a barrier to the process because it needs to be dynamic before adding the mirror)

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    Dynamic Data       992 KB    31 KB
  Partition 2    Dynamic Data       350 MB  1024 KB
  Partition 3    Dynamic Data       931 GB   351 MB
  Partition 4    Dynamic Data       728 KB   931 GB

If I look at diskpart documentation I see the following under "list partition"

Displays the partitions listed in the partition table of the current disk. On dynamic disks, these partitions may not correspond to the dynamic volumes on the disk. This discrepancy occurs because dynamic disks contain entries in the partition table for the system volume or boot volume (if present on the disk). Dynamic disks also contain a partition that occupies the remainder of the disk and reserves space for use by dynamic volumes.

From this I can presume that following:

  • Partition 1 is the EFI partition
  • Partition 2 is the MSR Partition
  • Partition 3 is my C drive
  • Partition 4 is partition that occupies the remainder of the disk.

Problem is that I can't create an EFI partition of 992 KB because the size for creating an efi partition is specified in MB.


    SIZE=<N>    The size of the partition in megabytes (MB). If no size is
                given, the partition continues until there is no more free
                space in the current region.

Is there any way to do this or am I interpreting the partitioning incorrectly?

  • THe problem is trying to create a 992kb partition. Why the heck do you want this? In times where disc sizes are that hugh, this is close to a feature noone needs. – TomTom Jan 5 '15 at 7:40
  • Because that is the size that the windows installer created when it built the boot drive and in order to mirror the partitioning scheme needs to be identical. – RonnBlack Jan 5 '15 at 15:24

The instructions you're trying to follow are for Windows Server 2008.

Windows 7 and newer (including Server 2012 and above) will format the EFI partition as FAT32, which has a minimum size limit of 65525 clusters. If your disk uses 512-byte block size, this works out to almost 32 MiB (33548800 bytes, to be exact). If your storage system uses 4 KiB blocks, then the required minimum size is almost 256 MiB (268390400 bytes).

The current Microsoft-recommended sizes for the EFI partition are 100 MiB for disks using 512-byte blocks, and 260 MiB for disks using 4 KiB blocks. For long-term server use, I'd consider setting up new system disks with a 260 MiB EFI partition in either case, if there's a possibility of the system migrating to storage with 4 KiB blocks in the future.

As a result, the supposed EFI partition size of 992 kb is simply incorrect for Windows Server 2012 R2. If the system was initially installed as Server 2003 and upgraded from there, it might have inherited the EFI partition created by an earlier implementation of Windows UEFI boot support, which had different requirements and might have used FAT12/FAT16 formatting on the EFI partition, which is no longer considered correct (but is not actively prevented from working).

If that is the case, you might need a third-party partitioning tools to reproduce the current system disk partition layout to the new disk. However, I would seriously consider any possibility to migrate the system to current standard layout instead, to prevent complications in future upgrades.

If your system uses UEFI native boot style, then the EFI partition needs to be recognizable to the firmware, i.e. its requirements won't change whether the OS uses a Dynamic Disk or not.


I would suggest trying the 2012 instructions from http://blogs.technet.com/b/tip_of_the_day/archive/2014/10/10/tip-of-the-day-configuring-disk-mirroring-for-windows-server-2012.aspx

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