1. はじめに

sdp profileがサポートされることにより、250GB以上のboot diskもサポートされるようになりました。　試しに1500GBで注文したサーバーが以下の通り。

注文時のBoot Volumeの構成(1500GB)

でも、、、

あれ、1500GBはどこに行った？
Cドライブは100GBしか認識していない。その後ろは割り当てされていない領域や、Dドライブやリカバリー領域など、混在している。

Cドライブを拡張しようとしても、後ろにDドライブやリカバリー領域があるため、Windowsの標準機能ではそのままでは拡張できません（3rd Partyツールであればサポートしているものもあるようです）。正直綺麗とは言い難い構成です。なお、DドライブはUEFIブートのための領域のようです。単体のイメージでBIOS/MBRとUEFI/GPTをサポートするためにこういう構成になっているのでしょう。

なんじゃこりゃ！？って思ったら、以下のようなdocsの記述と手順がありました。どうやらDドライブやRecovery領域は削除し、Cドライブを拡張した後に、再度Recovery領域を作成すれば良いようです。しかし、このdocsの通りやってもRecovery領域を回復できないので、事前にRecovery領域をコピーしておくといったアレンジをしてみました。
https://cloud.ibm.com/docs/vpc?topic=vpc-troubleshooting-unexpandable-c-drive

方針は以下の通りです。

Dドライブを削除（sdp profileを使っている場合、本稿執筆時点ではBIOS/MBRで起動してきている。少なくとも2TB以内であればUEFI/GPTにする必要はない。将来的にsecure bootなどがサポートされるようになったらまた再考が必要だが、少なくとも本稿執筆時点ではsdp profileではsecure bootはサポートされていない。）
Recovery Partitionをバックアップをしておき、Cドライブを広げた後に、再構築

2. 拡張手順

Recovery領域の確認

PS C:\> reagentc /info
Windows Recovery Environment (Windows RE) and system reset configuration
Information:

    Windows RE status:         Enabled
    Windows RE location:       \\?\GLOBALROOT\device\harddisk0\partition4\Recovery\WindowsRE
    Boot Configuration Data (BCD) identifier: 31a07952-4143-11f0-9c1d-0800277b2ea2
    Recovery image location:
    Recovery image index:      0
    Custom image location:
    Custom image index:        0

REAGENTC.EXE: Operation Successful.s

DISK構成の確認

PS C:\> Get-Disk | sort Number | ft -Auto

Number Friendly Name      Serial Number                        HealthStatus OperationalStatus Total Size Partition Style
------ -------------      -------------                        ------------ ----------------- ---------- ---------------
0      Red Hat VirtIO     02e7-32b820fe-8db2-4                 Healthy      Online               1.46 TB MBR
1      Red Hat VirtIO     cloud-init-                          Healthy      Online                 44 KB RAW
2      QEMU QEMU HARDDISK cloud-init-02e7_5058d21c-c282-4b80-9 Healthy      Online                380 KB RAW

PS C:\> diskpart

Microsoft DiskPart version 10.0.26100.1150

Copyright (C) Microsoft Corporation.
On computer: SYASUDA-WIN25

DISKPART> list disk

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0    Online         1500 GB      0 B
  Disk 1    Online           44 KB    44 KB
  Disk 2    Online          380 KB   380 KB

DISKPART> select disk 0

Disk 0 is now the selected disk.

DISKPART> list volume

  Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
  ----------  ---  -----------  -----  ----------  -------  ---------  --------
  Volume 0                      NTFS   Partition    100 MB  Healthy    System
  Volume 1     C                NTFS   Partition     98 GB  Healthy    Boot
  Volume 2     D                FAT32  Partition    200 MB  Healthy
  Volume 3         Windows RE   NTFS   Partition    887 MB  Healthy    Hidden

DISKPART> list partition

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    Primary            100 MB  1024 KB
  Partition 2    Primary             98 GB   101 MB
  Partition 3    Primary            200 MB    98 GB
  Partition 4    Recovery           887 MB    99 GB

Recovery領域にDrive Letter Rを割り当てる

DISKPART> select partition 4

Partition 4 is now the selected partition.

DISKPART> assign Letter=R

DiskPart successfully assigned the drive letter or mount point.

DISKPART> list volume

  Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
  ----------  ---  -----------  -----  ----------  -------  ---------  --------
  Volume 0                      NTFS   Partition    100 MB  Healthy    System
  Volume 1     C                NTFS   Partition     98 GB  Healthy    Boot
  Volume 2     D                FAT32  Partition    200 MB  Healthy
* Volume 3     R   Windows RE   NTFS   Partition    887 MB  Healthy    Hidden

DISKPART> exit

リカバリー領域のコピー


PS C:\> mkdir C:\backup


    Directory: C:\


Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d-----          6/5/2026   4:03 AM                backup


PS C:\> mkdir C:\backup\WindowsRE


    Directory: C:\backup


Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d-----          6/5/2026   4:03 AM                WindowsRE


PS C:\> robocopy R:\Recovery\WindowsRE C:\backup\WindowsRE /E /COPYALL /R:1 /W:1

-------------------------------------------------------------------------------
   ROBOCOPY     ::     Robust File Copy for Windows
-------------------------------------------------------------------------------

  Started : Friday, June 5, 2026 4:04:04 AM
   Source : R:\Recovery\WindowsRE\
     Dest : C:\backup\WindowsRE\

    Files : *.*

  Options : *.* /S /E /COPYALL /R:1 /W:1

------------------------------------------------------------------------------

                           4    R:\Recovery\WindowsRE\
100%        New File               3.0 m        boot.sdi
100%        New File                1155        ReAgent.xml
            New File                   0        SrSettings.ini
100%        New File             659.5 m        winre.wim

------------------------------------------------------------------------------

               Total    Copied   Skipped  Mismatch    FAILED    Extras
    Dirs :         1         0         1         0         0         0
   Files :         4         4         0         0         0         0
   Bytes :  662.56 m  662.56 m         0         0         0         0
   Times :   0:00:09   0:00:09                       0:00:00   0:00:00


   Speed :           73,386,382 Bytes/sec.
   Speed :            4,199.203 MegaBytes/min.
   Ended : Friday, June 5, 2026 4:04:14 AM

PS C:\> dir C:\backup\WindowsRE -Force


    Directory: C:\backup\WindowsRE


Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
---hs-          4/1/2024   2:00 AM        3170304 boot.sdi
---hs-          6/5/2026   3:34 AM           1155 ReAgent.xml
---hs-        10/14/2025  11:11 PM              0 SrSettings.ini
---hs-         5/15/2026   6:25 AM      691577427 winre.wim

Recovery 領域の無効化

PS C:\> reagentc /disable
REAGENTC.EXE: Operation Successful.

PS C:\> reagentc /info
Windows Recovery Environment (Windows RE) and system reset configuration
Information:

    Windows RE status:         Disabled
    Windows RE location:
    Boot Configuration Data (BCD) identifier: 00000000-0000-0000-0000-000000000000
    Recovery image location:
    Recovery image index:      0
    Custom image location:
    Custom image index:        0

REAGENTC.EXE: Operation Successful.

PS C:\> reagentc /info
Windows Recovery Environment (Windows RE) and system reset configuration
Information:

    Windows RE status:         Enabled
    Windows RE location:       \\?\GLOBALROOT\device\harddisk0\partition4\Recovery\WindowsRE
    Boot Configuration Data (BCD) identifier: 31a07952-4143-11f0-9c1d-0800277b2ea2
    Recovery image location:
    Recovery image index:      0
    Custom image location:
    Custom image index:        0

REAGENTC.EXE: Operation Successful.

パーティション4（リカバリー領域の削除）

PS C:\> diskpart

Microsoft DiskPart version 10.0.26100.1150

Copyright (C) Microsoft Corporation.
On computer: SYASUDA-WIN25

DISKPART> select disk 0

Disk 0 is now the selected disk.

DISKPART> list partition

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    Primary            100 MB  1024 KB
  Partition 2    Primary             98 GB   101 MB
  Partition 3    Primary            200 MB    98 GB
  Partition 4    Recovery           887 MB    99 GB

DISKPART> select partition 4

Partition 4 is now the selected partition.

DISKPART> delete partition override

DiskPart successfully deleted the selected partition.

パーティション3（Dドライブ）の削除

DISKPART> select partition 3

Partition 3 is now the selected partition.

DISKPART> delete partition override

DiskPart successfully deleted the selected partition.

DISKPART> list partition

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    Primary            100 MB  1024 KB
  Partition 2    Primary             98 GB   101 MB

Cドライブ（パーティション2）の拡張

DISKPART> select partition 2

Partition 2 is now the selected partition.

DISKPART> extend

DiskPart successfully extended the volume.

DISKPART> list partition

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    Primary            100 MB  1024 KB
* Partition 2    Primary           1499 GB   101 MB

DISKPART> list volume

  Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
  ----------  ---  -----------  -----  ----------  -------  ---------  --------
  Volume 0                      NTFS   Partition    100 MB  Healthy    System
* Volume 1     C                NTFS   Partition   1499 GB  Healthy    Boot

Cドライブから1000MB割り当ててRecovery領域を作成

DISKPART> shrink minimum=1000

DiskPart successfully shrunk the volume by: 1000 MB

DISKPART> create partition primary

DiskPart succeeded in creating the specified partition.

DISKPART> format quick fs=ntfs label=Recovery

  100 percent completed

DiskPart successfully formatted the volume.

DISKPART> set id=27

DiskPart successfully set the partition ID.

DISKPART> list partition

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    Primary            100 MB  1024 KB
  Partition 2    Primary           1498 GB   101 MB
* Partition 3    Recovery          1000 MB  1499 GB

DISKPART> list volume

  Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
  ----------  ---  -----------  -----  ----------  -------  ---------  --------
  Volume 0                      NTFS   Partition    100 MB  Healthy    System
  Volume 1     C                NTFS   Partition   1498 GB  Healthy    Boot
* Volume 2         Recovery     NTFS   Partition   1000 MB  Healthy    Hidden

Drive Letter Rを割り当ててリストアを実施

DISKPART> assign letter=R

DiskPart successfully assigned the drive letter or mount point.

DISKPART> list volume

  Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
  ----------  ---  -----------  -----  ----------  -------  ---------  --------
  Volume 0                      NTFS   Partition    100 MB  Healthy    System
  Volume 1     C                NTFS   Partition   1498 GB  Healthy    Boot
* Volume 2     R   Recovery     NTFS   Partition   1000 MB  Healthy    Hidden

DISKPART> exit

PS C:\> robocopy C:\backup\WindowsRE R:\Recovery\WindowsRE /E /COPYALL /R:1 /W:1

-------------------------------------------------------------------------------
   ROBOCOPY     ::     Robust File Copy for Windows
-------------------------------------------------------------------------------

  Started : Friday, June 5, 2026 4:17:01 AM
   Source : C:\backup\WindowsRE\
     Dest : R:\Recovery\WindowsRE\

    Files : *.*

  Options : *.* /S /E /COPYALL /R:1 /W:1

------------------------------------------------------------------------------

          New Dir          4    C:\backup\WindowsRE\
100%        New File               3.0 m        boot.sdi
100%        New File                1155        ReAgent.xml
            New File                   0        SrSettings.ini
100%        New File             659.5 m        winre.wim

------------------------------------------------------------------------------

               Total    Copied   Skipped  Mismatch    FAILED    Extras
    Dirs :         1         1         0         0         0         0
   Files :         4         4         0         0         0         0
   Bytes :  662.56 m  662.56 m         0         0         0         0
   Times :   0:00:10   0:00:10                       0:00:00   0:00:00


   Speed :           69,363,906 Bytes/sec.
   Speed :            3,969.035 MegaBytes/min.
   Ended : Friday, June 5, 2026 4:17:11 AM

PS C:\> dir R:\Recovery\WindowsRE -force


    Directory: R:\Recovery\WindowsRE


Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
---hs-          4/1/2024   2:00 AM        3170304 boot.sdi
---hs-          6/5/2026   3:34 AM           1155 ReAgent.xml
---hs-        10/14/2025  11:11 PM              0 SrSettings.ini
---hs-         5/15/2026   6:25 AM      691577427 winre.wim

PS C:\> reagentc /setreimage /path R:\Recovery\WindowsRE
Directory set to: \\?\GLOBALROOT\device\harddisk0\partition3\Recovery\WindowsRE

REAGENTC.EXE: Operation Successful.

PS C:\> reagentc /enable
REAGENTC.EXE: Operation Successful.

PS C:\> reagentc /info
Windows Recovery Environment (Windows RE) and system reset configuration
Information:

    Windows RE status:         Enabled
    Windows RE location:       \\?\GLOBALROOT\device\harddisk0\partition3\Recovery\WindowsRE
    Boot Configuration Data (BCD) identifier: 31a07954-4143-11f0-9c1d-0800277b2ea2
    Recovery image location:
    Recovery image index:      0
    Custom image location:
    Custom image index:        0

REAGENTC.EXE: Operation Successful.

Dirve Letterを削除

PS C:\> diskpart

Microsoft DiskPart version 10.0.26100.1150

Copyright (C) Microsoft Corporation.
On computer: SYASUDA-WIN25

DISKPART> list disk

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0    Online         1500 GB      0 B
  Disk 1    Online           44 KB    44 KB
  Disk 2    Online          380 KB   380 KB

DISKPART> select disk 0

Disk 0 is now the selected disk.

DISKPART> list volume

  Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
  ----------  ---  -----------  -----  ----------  -------  ---------  --------
  Volume 0                      NTFS   Partition    100 MB  Healthy    System
  Volume 1     C                NTFS   Partition   1498 GB  Healthy    Boot
  Volume 2     R   Recovery     NTFS   Partition   1000 MB  Healthy    Hidden

DISKPART> list partition

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    Primary            100 MB  1024 KB
  Partition 2    Primary           1498 GB   101 MB
  Partition 3    Recovery          1000 MB  1499 GB

DISKPART> select partition 3

Partition 3 is now the selected partition.

DISKPART> remove letter=R

DiskPart successfully removed the drive letter or mount point.

DISKPART> list volume

  Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
  ----------  ---  -----------  -----  ----------  -------  ---------  --------
  Volume 0                      NTFS   Partition    100 MB  Healthy    System
  Volume 1     C                NTFS   Partition   1498 GB  Healthy    Boot
* Volume 2         Recovery     NTFS   Partition   1000 MB  Healthy    Hidden

DISKPART> exit

Leaving DiskPart...

3. 最終完成系

Cドライブが拡張され、その一番最後にRecovery領域が作成されている。

4. Recovery領域の動作確認

次回起動時にRecovery領域を使ってBoot

PS C:\> reagentc /boottore
REAGENTC.EXE:  Operation Successful.

再起動

PS C:\> shudown /r /t 0

VNCコンソールでRecoveryモードになっていることを確認