Windows 7: Backing up to a hard drive and a DVD: big image size differences?

I've backed up Windows through the official Windows Backup tool (in the Control Panel) to a hard drive (actually, a second partition). It takes about 8-12 GB (don't remember correctly). Then, right after that, I chose to make a backup also on a DVD, and, surprisingly, one DVD was enough!
First of all, it's weird that it could fit into one DVD while if I tried to burn the files form the backup on the hard drive, I would need at least two. And then the second thing: the files on the DVD all take about 3.4 GB. I tried making an image of it though Alcohol 120, and the MDF file takes about 3.4 GB. ImgBurn couldn't make an image, because it's a multiple session DVD.
So why is there such a difference in size between system images backed up to the hard drive and a DVD? Can I trust a DVD?


By the way, I tried creating backup with Arconis True Image (I don't remember true name) and Norton Ghost 15 to a hard drive, and their images take about 3 GB. So if the real size of my system image is about 3 GB, then why did Windows backup on HDD take so much place?



It's Windows 7 Ultimate 32 bit, by the way.

I'm thinking it has to do with how much compression was used by the different backup/imaging programs. As far as trusting a DVD, I'd say it depends on which imaging tool you use (native Windows 7, Acronis, Macrium, etc) and what kind of DVD you use (-R. +R, -RW, +RW). The Windows 7 imaging tool has a history of being very tempermental. Sometimes it works with a DVD, sometimes it doesn't.

Windows 7 Fails to create Backup Image on DVD-R. DVD-RW OK - Microsoft Answers

As far as saving an image on a different partition of your hard drive, I'm totally against that. If the drive fails, you probably won't be able to access the image. So that's just about like having no image at all. I think an external hard drive is the best way to save your images. As you get more programs and data on your hard drive you'll probably need multiple DVDs to do an image. One bad burn to a DVD and your image again becomes worthless. An external hard drive will let you save multiple images increasing the odds that you'll always have a good image to fall back on. Just my opinion.

Compression is one factor. What is backed up is another.

If you perform a system image backup, then there is no compression of the backed up drives other than elimination of such things as pagefiles, hibernation files, temp files, and space saved due to elimination of fragmentation.

The system image process creates a Virtual Hard Drive (VHD) file and other accompanying info to facilitate reconstruction of partitions when necessary.

The file backup portion of Win 7 Backup and Restore creates ZIP files. They are not highly compressed.

Win 7 backup and restore offers two types of backups either separately or as part of the same backup, that is, there can be an image backup and an additional separate file backup via ZIP files.

I use Win 7 backup and restore for system image backups. The VHD approach is a very flexible approach. Incidentally, you can clean up your hard drive by making a system image backup and then running Win 7 Restore from a System Repair Disc. This will give you an unfragmented system with the elimination of temp files, etc.

I do not use Win 7 for this reason, however, if you ever decide to perform a Wiin 7 system image backup and restore, then you might want to compare the free space before and after.

I have to clarify one thing: I did use native Windows 7 Backup and Restore utility to make two backups (one after another, without doing any other tasks). The first was backup to another partition, the second was backup to DVD. I mean, the same program made backup of the same system withing a span of some minutes and their sizes differ much. Could have it used different compression levels according to the level of free space on destination locations?

In other words, since images by Ghost and Arconis are of the similar size as a DVD backup made by Windows Backup and Restore, I assume the Windows Backup and Restore made DVD is good - question is why the image saved by the very same Backup and Restore to a hard drive is more than twice as big as the one made directly to the DVD...

2) Let's say, I want to use the image that Windows 7 Backup and Restore saved on my hard drive (which is more than 8 GB). Will the restore work if I burn those files to a BD-R, or do they have to be on some sorf of a hard drive (or network)?

I'm not a good butterfly chaser.

Presently, there is no problem.