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Accessing Raw Partitions in Virtualbox

I just wanted to resize an NTFS partition in Linux just to realize, that gparted had some problems resizing. Maybeit was an unclean unmount or a necessary chkdisk session. who knows.

The solution I had in mind was to simply "mount"; the partition inside a Windows 7 VM running in Virtualbox. Giving Windows 7 raw access to the partition should enable it to do its Windows NTFS specific stuff and even resize the partition for me.

First of all: enable read/write operations on the partition for my "normal"; user (because this is where VirtualBox will get its privileges from)

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$ sudo chmod 777 /dev/sda3

After that, simply use the "VBoxManage"; utility (pay attention to the capitalization) utility to create a vmdk file pointing to the partition:

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VBoxManage internalcommands createrawvmdk -filename /ntfs.vmdk -rawdisk /dev/sda -partitions 3 -relative -register

This will create a file called ntfs.vmdk (and a ntfs-pt.vmdk) that point to the /dev/sda3 partition (which is the NTFS partition in question) and register it within the virtualbox harddisk manager thingy

The resulting vmdk file will probably look something like this:

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$ cat WinHD.vmdk 
# Disk DescriptorFile
version=1
CID=108af78c
parentCID=ffffffff
createType="partitionedDevice"

# Extent description
RW 63 FLAT "WinHD-pt.vmdk"
RW 157581522 ZERO 
RW 551109825 FLAT "/dev/sda3"
RW 63 FLAT "WinHD-pt.vmdk" 63
RW 265377672 ZERO 
RW 63 FLAT "WinHD-pt.vmdk" 126
RW 2698857 ZERO 
RW 5103 ZERO 

# The disk Data Base 
#DDB

ddb.virtualHWVersion = "4"
ddb.adapterType="ide"
ddb.geometry.cylinders="16383"
ddb.geometry.heads="16"
ddb.geometry.sectors="63"
ddb.uuid.image="d22d1f60-8f49-4050-94b4-ac427899a2e2"
ddb.uuid.parent="00000000-0000-0000-0000-000000000000"
ddb.uuid.modification="70447f47-959f-4ccd-a9a3-a0c1b699dd85"
ddb.uuid.parentmodification="00000000-0000-0000-0000-000000000000"
ddb.geometry.biosCylinders="1024"
ddb.geometry.biosHeads="255"
ddb.geometry.biosSectors="63"

Next thing to do: Then simply add the created new vmdk image to your VM in question. This can be done via GUI or on the commandline:

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VBoxManage modifyvm win7 --hdb /home/marc/WinHD.vmdk

After doing that, you should be able to simply boot your VM and have chkdsk/whatever do it's magic.

p.s. as usual: this could destroy your partitions yadda yadda yadda

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