- Upon Checking, a Big Surprise Is Possible
- Managing Restore Point Space in Windows 7 Through the GUI
- Managing Restore Point Space at the Command Line
Among its many and varied system protection capabilities, Windows 7 makes restore points of the drives under its management. At a minimum, this means a new restore point is captured no less than every 7 days by default. Under normal operating conditions, with occasional Windows Updates, driver updates, software installs, and so forth, users may generate as many as half-a-dozen restore points in an average week.
If you use a disk inspection tool like the excellent (and free) WinDirStat, you can instruct the program to show you how much disk space is going to what is known in Windows-speak as the Volume Shadow Copy Service (usually abbreviated as VSS, for Volume Shadow Service).
Figure 1 shows the "Unknown" file block (which is how restore points appear in WinDirStat once you check the check box in the Options menu labeled "Show Unknown").
Figure 1 On my test system, restore points currently occupy 3.3 GB of disk space.
Upon Checking, a Big Surprise Is Possible
I first became aware of this hidden form of disk consumption back in 2006, right after I installed my first great big 500 GB hard disk. In checking free space for the drive right after OS installation and initial setup, I was surprised to see a 69 GB discrepancy between how much space I thought I should have free (the difference between total available space and space actually consumed for visible files on the hard disk).
It turns out that Vista reserves 15 percent of a hard disk's capacity for restore points and Volume Shadow Copy items by default, and that's exactly where the missing space had gone, thanks to my migration of a huge collection of music files from an older system drive to the current one.
After some research, this work led me to WinDirStat, which showed me that the space was being consumed at Vista's direction, and helped me figure out what role it served in protecting my system. I just happened to create a perfect set of conditions in which the entire amount of space that gets allocated for shadow copies was actually consumed. In most cases, the actual space consumed will be less than the maximum amount of space reserved for restore points and other shadow copy items.
If you upgrade a system from Windows Vista to Windows 7, it will not resize the space allocated for shadow copies. Thus, even though Windows 7 consumes only 5 percent of disk space for shadow copy items by default, the drive to which the upgrade is applied will continue to allocate 15 percent of available space for such uses.
When Does It Make Sense to Alter Shadow Copy Space Allocations?
As described, when a Vista system disk is upgraded to Windows 7, it makes sense to readjust volume shadow copy space allocation. Also, whenever you plan to migrate from a larger drive to a smaller one by copying a drive image from source to target, you'll want to adjust the volume shadow space allocation in advance of that move. Though you can do it after the fact, why copy gigabytes of restore points and other volume shadow items from the old drive to a new one, only to delete them sometime soon thereafter?
On the other hand, any time you either want or need more free space on a system drive for any reason, you can trim your volume shadow space allocation as a quick and easy way to reduce the space that files already occupy on that drive. It is a trade-off, though, because you don't want to find yourself in the situation of needing a restore point that is no longer available with no other recourse. That's why I recommend making an image backup of your system drive before you start whittling away at volume shadow space allocations.