Thanks for the heads up on this. If the data blocks don't have anything written into them, then what data is written into them when using dd? if I restore the dd image will the blocks then be in the same state i.e unwritten to? Also following on from this if I create a file using dd let's say 2GB, how does the filesystem know that all these blocks belong to the file myfile.img, and where is the information stored to say that a block has data written into it or not? Thanks Dan On Wed, Jun 25, 2008 at 12:48 PM, Chris G <cl@xxxxxxxx> wrote: > On Wed, Jun 25, 2008 at 12:27:04PM +0100, Dan Track wrote: >> Hi >> >> I've got a xen vm file called test, if I copy it with dd I get the following >> dd if=/opt/xen/test of=/opt/test-vm.img bs=4096 >> du -s /opt/xen/test = 1934112 >> du -s /opt/test-vm.img = 26240040 >> >> My question is why is the test-vm.img larger in size than the original? >> > Perhaps because the original file is 'sparse', i.e. it has large > unused chunks in it, when originally created these will be unallocated > and use no space, only when written to will the space be allocated. > However when you dd the file it writes everything (including 'nul' > data) to the destination file. > > -- > Chris Green > > -- > fedora-list mailing list > fedora-list@xxxxxxxxxx > To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list > -- fedora-list mailing list fedora-list@xxxxxxxxxx To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list
