vhd sorry there was a problem mounting the file

If we go through the format then reading and writing (at block level) is possible.Some Windows users may receive an error message “Sorry, there was a problem mounting the file” when trying to mount an ISO or IMG file.

Writing to the child additionally requires updating the 512 byte sector bitmap.Įvery virtualized image container has similar schemes to represent disk blocks in a sparse fashion. The relationship on who's the parent and who's the child are again present in the dynamic VHD's header. Meaning, if there's a linked differencing child VHD then we should apply the above process on the child and not the base.

Please bear in mind that this scheme is valid only for dynamic VHDs which are not linked. In such scenario, you need to append a new data block to the dynamic VHD, update the BAT entry to point to the start of this block (the 512 sector) and then update the dynamic header and footer's CRC field since we have updated the BAT (CRC is over it). It is quite possible that the BAT does not have an entry for the logical disk block that you need to write to. The VHD file offset which you get at this point is the offset where you need to write to given the input, logical disk offset. skip the sector bitmap which precedes every block). So all we have to do is: find the 'VHD file offset' of the logical block which we need to write to using the entry for the 2MB logical window present in the BAT. BAT entries (unlike how data blocks are potentially positioned non-sequentially) are ordered and contain the dynamic VHD file offset of the corresponding container data block. The mapping of which VHD block corresponds to which physical disk window is maintained in the Block Allocation Table. Meaning: In dynamic VHD image, a 2MB (physical) disk window could potentially reside (in the dynamic VHD) after a 2MB disk window which in the actual disk would always be physically before the first 2 MB window. The dynamic VHD representation of this physical disk is essentially a sequence of such 2MB blocks, in no particular order. Specifically, for dynamic VHDs, the entire length of the physical disk is divided into logical 2MB windows. As long you don't touch this trailing footer the raw block level edits (manual or programmatic) should be fine.įor dynamic VHDs or any other sparse representation of a physical disk, the task boils down to translating logical disk offsets into the 'container' file offsets. For a 'fixed' VHD you could, as you said : 'just take a textfile or another file an write the bytes in it exactly to a disk.' Fixed VHDs are just flat disk images plus a 512 footer at the end.

Vhd sorry there was a problem mounting the file