To clone a partition using dd.exe which comes with MSYS2 for Windows, we require 3 pieces of information.
- physical drive name
- partition starting offset (in MiB)
- partition size (in MiB)
dd if=physical_drive_name of=backup.img bs=1M skip=starting_offset count=size status=progress
To list available physical disk drives, we can use the command:
wmic diskdrive get Caption,Index,MediaType
On my system, it outputs:
Caption Index MediaType
PC SN530 NVMe WDC 512GB 0 Fixed hard disk media
PNY USB 3.0 FD USB Device 1 Removable Media
I am interested in my NVMe drive, so I will use its index (0) to find requirement #1 which is physical drive name:
wmic diskdrive where "Index=0" get DeviceID,Partitions,Status,MediaLoaded
it outputs:
DeviceID MediaLoaded Partitions Status
\.PHYSICALDRIVE0 TRUE 8 OK
The 2 other requirements are partition starting offset and partition size. To list partitions and their attributes, I’ll use the command:
wmic partition where "DiskIndex=0" get Name,Index,Type,StartingOffset,BlockSize,NumberOfBlocks,Size
It outputs:
BlockSize Index Name NumberOfBlocks Size StartingOffset Type
512 0 Disk #0, Partition #0 614400 314572800 1048576 GPT: System
512 1 Disk #0, Partition #1 727875584 372672299008 449839104 GPT: Basic Data
512 2 Disk #0, Partition #2 225282048 115344408576 373123186688 GPT: Basic Data
512 3 Disk #0, Partition #3 102400 52428800 488467595264 GPT: Basic Data
512 4 Disk #0, Partition #4 2123776 1087373312 488520024064 GPT: Unknown
512 5 Disk #0, Partition #5 2027520 1038090240 489609494528 GPT: Unknown
512 6 Disk #0, Partition #6 39032832 19984809984 490647584768 GPT: Unknown
512 7 Disk #0, Partition #7 2883584 1476395008 510633443328 GPT: Unknown
So now, we can use the starting offset and size of the partition of our choice with dd.exe to clone it. However, this output does not give us a hint on the contents of the partitions. For that, we need to list volumes so that we can view the filesystems and labels of formatted partitions:
wmic volume where "DriveType=3" get Label,DeviceID,DriveLetter,DriveType,SerialNumber,FileSystem,MaximumFileNameLength,BlockSize,Capacity,FreeSpace
It outputs:
BlockSize Capacity DeviceID DriveLetter DriveType FileSystem FreeSpace Label MaximumFileNameLength SerialNumber
4096 372672294912 \?Volume{41d21340-a487-4021-9735-3e999ccfc734} C: 3 NTFS 232339791872 OS 255 3295242676
\?Volume{e5ffe5ea-3596-468c-832f-e5bcf2aeb39e} 3
512 48234496 \?Volume{5792630e-1c80-4d8a-a679-82ec4cd0ecdc} 3 FAT32 39666176 GRUBX64 255 716055397
4096 1087369216 \?Volume{19df495f-4e17-41fb-bcb0-d33d40588153} 3 NTFS 161165312 255 1445116501
4096 1038086144 \?Volume{9e1ca148-9cff-4576-ba37-cad1aab53ba1} 3 NTFS 501415936 WINRETOOLS 255 4141927052
4096 19984805888 \?Volume{0e8ffde2-0844-4d79-ada2-a3ea534dcc6b} 3 NTFS 136228864 Image 255 3940616972
4096 1476390912 \?Volume{a847a1f9-be5e-4f38-80ff-e5617868e2a1} 3 NTFS 505286656 DELLSUPPORT 255 1554162235
4096 310378496 \?Volume{9685da03-f3a8-4f89-88f2-1b9dafc3bd38} 3 FAT32 203812864 ESP 255 684405683
Now if we can determine the partition number of the volume of our interest, we can refer to the partition table to find the starting offset and size to use them with dd.exe, but how can we do that?
The reliable (unique) volume attributes are serial number, deviceID and (label and drive letter if any). size in general is not reliable as 2 or more partitions may have the same size.
Suppose the volume of our interest is DELLSUPPORT, how do we find its partition number so that we can find its starting offset and size to use with dd.exe?
1
I found a solution using Powershell:
1-List physical disks:
Get-Disk
2-List partitions of disk number 0:
Get-Partition -DiskNumber 0
3-List volumes on disk number 0 partitions :
Get-Partition -DiskNumber 0 | Get-Volume
4-Include FileSystemType and FriendlyName volume attributes in the partition table:
Get-Partition -DiskNumber 0 | Select-Object PartitionNumber,DriveLetter,Offset,Size,type,
@{Name="FileSystemType";Expression={(Get-Volume -Partition $_).FileSystemType}},
@{Name="FriendlyName";Expression={(Get-Volume -Partition $_).FileSystemLabel}} | Format-Table -AutoSize
To copy disk with dd you do not need a physical drive name. You need to specify a source file, but would that be a physical drive name, logical drive name or an actual file – does not matter.
If you want to make a backup of a partition, you need to specify a logical name for that partition. To get them, you need to use a standard tool fdisk:
# to get all partitions of all physical disks:
fdisk -l
# to get partitions just for the primary hard drive:
fdisk -l /dev/sda
Another wrong assumption about dd: You do not need to specify partition start and size. If you want a whole partition – you just need a name. If you specify start and size – you will get just a segment of that partition.
So to make a backup of the boot partition all you need is:
dd if=/dev/sda1 of=backup.img
Also it is not a good idea to mix tool chains (dd is from msys2, wmic is from windows management). Possible, but leads to a lot of confusions and unnecessary conversion of data. If you started to use msys2 tools – use them. If wmic is more to your liking – use windows’ own backup tools.