Is making an image of a DVD disk faster than copying DVD on disk?
In theory making an image of the DVD should be faster than just copying the files and directories, since the image copy is done on a sector-by-sector basis and does not waste time on following the files through the file system.
There are no numbers that I could find for reading the DVD, but some burner programs claim that writing an iso is 6-7 times faster than copying the files/directories. It seems logical that the reverse operation should also be faster for the same reason.
Yes, making an image on the harddrive will be faster. The bottleneck in the above situation is DVD write/read speed. Writing to the harddrive is significantly faster than writing to physical media like DVD's.
So, you have the two scenarios:
1) Read from DVD and write to HDD.
If your drive is a standard 16X DVD-RW drive, then this should take about (4.7GB / 22MB/sec) = 3.7 minutes. We can consider the HDD write speed to be negligable because it will be done at the same time as the reading of the DVD and can easily keep up.
2) Read from DVD, store temporarily on hard drive and finally write to DVD.
Similarly, in this case you have to do the same thing as above and write back to the disc. If you write speed is also 16x then you are looking at a total of 7.4 minutes.
In the first case you only have to read from the DVD once where as in the second, you'll have to both read from the DVD, write to the hdd and finally write to a DVD which takes more time.