Shadow Copies
45
NAS 1500s and 500s Administration Guide
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 and other backup programs that use shadow copy
technology because these programs are also limited to using the amount of disk space
specified by administrators.
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.
The minimum amount of storage space that can be specified is 100 megabytes (MB). The
default storage size is 10% of the source volume (the volume being copied). If the shadow
copies are stored on a separate volume, change the default to reflect the space available on the
storage volume instead of the source volume. Remember that when the storage limit is
reached, older versions of the shadow copies are deleted and cannot be restored.
When determining the amount of space to allocate for storing shadow copies, consider both
the number and size of files that are being copied, as well as the frequency of changes between
copies. For example, 100 files that only change monthly require less storage space than 10
files that change daily.
To change the storage volume, shadow copies must be deleted. The existing file change history
that is kept on the original storage volume is lost. To avoid this problem, verify that the storage
volume that is initially selected is large enough.
When using a basic disk as a storage area for shadow copies and converting the disk into a
dynamic disk, it is important to take the following precaution to avoid data loss:
■
If the disk is a non-boot volume and is a different volume from where the original files
reside, first dismount and take offline the volume containing the original files before
converting the disk containing shadow copies to a dynamic disk.
■
The volume containing the original files must be brought back online within 20 minutes,
otherwise, the data stored in the existing shadow copies is lost.
■
If the shadow copies are located on a boot volume, the disk to can be converted to dynamic
without losing shadow copies.
Note:
Use the mountvol command with the /p option to dismount the volume and take it offline.
Mount the volume and bring it online using the mountvol command or the Disk Management
snap-in.
