Why image size > size of the disk from which it is created?
Posted: Thu May 03, 2012 4:51 pm
I created an image form a USB drive whose total disk size is 1,998,743,040 bytes (not the volume size; got from a WMI call to Win32-DiskDrive). The image size is 2,003,795,968 bytes (not the size on disk; got by checking the file's properties in Windows Explorer). As you can see, the image size is 5,016,928 bytes (5MB) bigger than the disk size. Why??
If the image file is an exact bit-mapped image sector by sector, it shoud be exactly the same size as the disk from which the image is created. I repeated testing this with several drives of different sizes and all the image files are a few MB bigger than the disks from which they are created! You can verify this your self. Just create an image using any USb drives you have. Take a note on the disk size and image file size, you will be puzzled like me!
Further more, if I restore these larger image files back to the same disks from which they were created, most of times it restored images back to the drives with no errors. But a few times, I got the error saying "the image file is too large for selected usb device".
This seems saying that an image file created from a drive may not always be resored to the drive from which the image was created!?
Can anyone explain this?
If the image file is an exact bit-mapped image sector by sector, it shoud be exactly the same size as the disk from which the image is created. I repeated testing this with several drives of different sizes and all the image files are a few MB bigger than the disks from which they are created! You can verify this your self. Just create an image using any USb drives you have. Take a note on the disk size and image file size, you will be puzzled like me!
Further more, if I restore these larger image files back to the same disks from which they were created, most of times it restored images back to the drives with no errors. But a few times, I got the error saying "the image file is too large for selected usb device".
This seems saying that an image file created from a drive may not always be resored to the drive from which the image was created!?
Can anyone explain this?