I have all my drives turned off of System Restore (Shadow Copy) except the C: drive. As you can see from the attached document from Microsoft Vista Help Files Shadow Copy takes up no more that 15% of the disk space. "System Restore doesn't protect FAT32 and other FAT disks because FAT disks don't support the use of shadow copies. Shadow copies contain information about changes to documents and system files. Shadow copies require the NTFS file system. In this version of Windows, System Restore uses shadow copies to create restore points. If you store system files on a FAT disk, you cannot use System Restore to undo changes. How much disk space does System Restore require? To store restore points, you need at least 300 megabytes (MB) of free space on each hard disk that has System Protection turned on. System Restore might use up to 15 percent of the space on each disk. As the amount of space fills up with restore points, System Restore will delete older restore points to make room for new ones. System Restore will not run on disks smaller than 1 gigabyte (GB) "
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