Re: [Qemu-devel] qemu dd sizes

[Kyle Hayes]

On Friday 24 September 2004 19:15, jmf wrote:
> When using dd to create a disk image to boot through qemu, does the
> block size really matter, or can I omit that parameter?  If the size of
> the original disk is 20 gb but there is only 2 gb of data on the disk,
> how can I make the image size smaller?

It is a little unclear what you are asking here.   dd uses the block size 
and a count in order to determine how much to copy.  If you are making a 
file with holes in it, you can use a block size, offset and then set 
count=0.  If you omit the count and block size, it will use the default 
block size (512 bytes I think) and will simply copy until either the 
source runs out of data or the destination runs out of space.

If there is 2GB, it depends what the original filesystem was.  Ext2/3 
(under Linux) puts data all over the disk in a sparse manner.  So, just 
copying the first 2GB would not get all the data.  If it is a Windows 
partition and you are using VFAT, then running the defragmenter program 
will push all the data to one end of the disk (beginning?).  With NTFS, 
I'm not sure what happens.

You could try to resize the 20GB partition down to 2.5GB and then copy that 
with dd.  What kind of filesystem is it?

Best,
Kyle