Allocating Disk Space for Shadow Copies
When shadow copies are enabled on a volume, the maximum amount of volume space to be used for the shadow copies can be specified. The default limit is 10 percent of the source volume (the volume being copied). The limit for volumes in which users frequently change files should be increased. Also, note that setting the limit too low causes the oldest shadow copies to be deleted frequently, which defeats the purpose of shadow copies and frustrates users.
If the frequency of changes to each file is greater than the amount of space allocated to storing shadow copies, then no shadow copy is created. Therefore, administrators should carefully consider the amount of disk space they want to set aside for shadow copies, and keep in mind user expectations of how many versions they will want to have available. End users might expect only a single shadow copy to be available, or they might expect three days or three weeks worth of shadow copies. The more shadow copies users expect, the more storage space administrators must allocate for storing them.
Setting the limit too low also affects backup programs that use shadow copy technology because these programs are also limited to using the amount of disk space specified by administrators.
The important point for administrators to understand is that the amount of disk space allocated for shadow copies depends on how frequently that data changes rather than how much data is being stored.
Note: Regardless of the volume space that is allocated for shadow copies, there is a maximum of 64 shadow copies for any volume. When the 65th shadow copy is taken, the oldest shadow copy is purged.
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