image Okay this was my problem with my new tablet since I have it only 2 weeks or so. But with 120GB it has really is left only 29-31GB which means I used about 70 GB already (5.5GB is being separated to another partition). All my programs are like 20 programs or so, including heavy-weight stuffs like Microsoft Office 2007 (625MB), Thunderbird DB (600MB), Eclipse (330MB), Photoshop CS2(210MB), PC-Doctor-5(130MB)--bundled with my tablet--I'm not quite sure what is really is :-P I'll give it a shot first. However, all these programs, including Vista business, and my data, are only 30GB. So where the heck is another 30G?

Let's see; I had tried with all my common sense and it came up with nothing; I felt like when I was finding the photos in my treo in FileZ; you couldn't see whether they are in memory at all! (if you are using Palm NVFS-based device, try by yourself; you'll see what I'm talking about) What I did is using Disk Cleanup, deleting all temp files, checking all the program that might related with backup/restore, turning off UAC, getting into safemode with admin account to find where that file is, and restarting many times. I still found no clue. You may see 2 figures below. That really conflicts with what my computer shown above!

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I hadn't known what the hidden 30GB file is until I googled it. I found that Vista has a whole new system of system restore, including new strange name--shadow copy storage. For Vista you couldn't adjust how large the storage for system restore is by GUI anymore. It shows only a bit information, and a check box to turn on/off. So what does the system restore differ to the old one on XP? I can say that they are practically the same but, on Vista, it's much more elegant and powerful (or too powerful, I guess)

"In Windows XP, System Restore uses a file system filter to keep track of system file changes. In Windows Vista, System Restore uses Volume Shadow Copy Service to keep track of block-level changes over the selected volumes."

shadow copy service was introduced in Windows Server 2003, I believe. It uses for keep tracking all the data and copy in this backup disk (which is invisible) This service is totally automatically--meaning that you can do nothing about this. However, the maximum shadow storage will be set based on the actual volume or the free space after setting up. It's usually up to 30% of free space or 15% the overall size of the volume. I found the typical computer has a maximum shadow storage about 15GB, but, frankly, my Thinkpad X61T doesn't have the maximum value, how odd!!? UNBOUNDED--that's what it set to mine. :-/

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Anyway, you could check the used, allocated, and maximum shadow copy storage by run elevated command prompt (start | type "cmd" | right-click on cmd.exe and tap Run as administrator)

vssadmin list shadowstorage

In case you want to change the maximum shadow storage, you could use the command

VSSAdmin Resize ShadowStorage /For=C: /On=C: /MaxSize=15GB

While For is the volume you want to backup, On is the where the shadow space is, MaxSize is a maximum size you want. If you are shrinking the volume, you may lose your previous backup as well, just to beware.

Now you know what shadow copy storage is. Then you will know how you can take the advantage of this service and you'll know how great this is. Practically, shadow will copy everything in every period you have changed anything to the disk. Thus, you will be able to restore what files/folders you want to be the way they were by easily right-click on that file/folder, then tap on "Restore previous versions"

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then you will see tons of file/folder you want to restore in many points of time.

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For me, with UNBOUNDED setting, I can roll up to the first day I got this tablet. The process is quite intuitive. I can't wait to try Time Machine in Leopard to see how good it is though.

All in all, this is such a great feature but it can't be great with *unbounded* setting for sure. You may try to find out how much shadow eating up your hard drive, then resize it. I have no idea why this happened, but, without this problem, I won't know that there is something running underneath and duplicating all my stuffs. I have about 3 computers with Vista now, I haven't found this bother me, perhaps it was set correctly. Therefore, I haven't noticed this invisible volume. Finally, I can think of many situation that found this really great tool, like accidentally delete the important file, or a file was intentionally deleted, but I need that file back. As long as it doesn't waste much space, it's a fantastic feature.

ps. I don't know if this bundled in Vista Home basic or premium or not, since these 2 don't have restore/backup capability. I'll let you know when I found out. But for Vista Business and Ultimate, you expect to have this :-)

Edited on Jan 23, 2008: Vista Home Premium does have Shadow Storage feature. Thus I think there is no reason why Home Basic would not include this useful feature as well.

reference: How Volume Shadow Copy Service Works, Volume Shadow Copy Service Overview, Windows Vista Backup Technology