HP ProLiant ML310 G3 Storage Server - Manual (Page 46)

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 350 megabytes (MB). The default storage
size is 10 percent 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.
CAUTION:
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.
Identifying the storage area
To store the shadow copies of another volume on the same file server, a volume can be dedicated on
separate disks. For example, if user files are stored on H:\, another volume such as S:\ can be used to
store the shadow copies. Using a separate volume on separate disks provides better performance and is
recommended for heavily used storage servers.
If a separate volume will be used for the storage area (where shadow copies are stored), the maximum
size should be changed to No Limit to reflect the space available on the storage area volume instead of
the source volume (where the user files are stored).
Disk space for shadow copies can be allocated on either the same volume as the source files or a
different volume. There is a trade-off between ease of use and maintenance versus performance and
reliability that the system administrator must consider.
By keeping the shadow copy on the same volume, there is a potential gain in ease of setup and
maintenance; however, there may be a reduction in performance and reliability.
CAUTION:
If shadow copies are stored on the same volume as the user files, note that a burst of disk input/output
(I/O) can cause all shadow copies to be deleted. If the sudden deletion of shadow copies is
unacceptable to administrators or end users, it is best to use a separate volume on separate disks to
store shadow copies.
Determining creation frequency
The more frequently shadow copies are created, the more likely that end users will get the version that
they want. However, with a maximum of 64 shadow copies per volume, there is a trade-off between the
frequency of making shadow copies and the amount of time that the earlier files will be available.
By default, the storage server creates shadow copies at 0700 and 1200, Monday through Friday.
However, these settings are easily modified by the administrator so that the shadow copy schedule can
better accommodate end user needs.
Shadow copies and drive defragmentation
When running Disk Defragmenter on a volume with shadow copies activated, all or some of the shadow
copies may be lost, starting with the oldest shadow copies.
If defragmenting volumes on which shadow copies are enabled, use a cluster (or allocation unit) size
of 16 KB or larger. Using this allocation unit size reduces the number of copy outs occurring on the
46 File server management