Ticket #9643 (closed enhancement: fixed)

Opened 5 years ago

Last modified 15 months ago

VBoxManage showhdinfo should show data alignment

Reported by: sven.koehler Owned by:
Priority: major Component: other
Version: VirtualBox 4.1.2 Keywords:
Cc: Guest type: other
Host type: other

Description (last modified by frank) (diff)


it would be very useful, if VBoxManage would show the alignment of the datablocks inside the VDI file. There are tools out there (CloneVDI, tool announced in the forums) which modify the alignment of the data such that sector 63 of the virtual harddisk is aligned to 4K. While this is good for Windows XP/DOS and the default partition layout, it is bad for Windows where partitions start at a 1MB boundary.

Also, there seem to be "old" VDI files, where data blocks are not aligned on a 4K boundary which AFAIK results in poor AIO/DIO performance. For example I have a flat VDI file with Windows 7 on it, where the MBR is at offset 0x20200 within the file (which is a 512 byte boundary, and not a 4KB boundary). I had to verify this using a hex editor.

I would suggest that VBoxManage shows

  • the offset of the first data block in the VDI file
  • the first sector of the virtual harddisk which is aligned to a 4K boundary (some value in the range of 0 to 7)

Change History

comment:1 Changed 5 years ago by frank

VBoxManage internalcommands dumphdinfo IMAGE prints out the data offset.

comment:2 Changed 15 months ago by frank

  • Status changed from new to closed
  • Resolution set to fixed
  • Description modified (diff)

The data offset is also shown by vbox-img (shipped with VBox 5.0.x).

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