HP AiO400r HP StorageWorks All-in-One Storage System User Guide (440583-006, J - Page 145

Identifying the storage area, Determining creation frequency, Shadow copies and drive defragmentation

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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 systems. 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 system 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 snapshot. Otherwise, the number of changes caused by the defragmentation process can cause shadow copies to be deleted faster than expected. Note, however, that NTFS compression is supported only if the cluster size is 4 KB or smaller. NOTE: To check the cluster size of a volume, use the fsutil fsinfo ntfsinfo command. To change the cluster size on a volume that contains data, back up the data on the volume, reformat it using the new cluster size, and then restore the data. HP StorageWorks All-in-One Storage System 145

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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 systems.
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 system 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
snapshot. Otherwise, the number of changes caused by the defragmentation process can cause
shadow copies to be deleted faster than expected. Note, however, that NTFS compression is supported
only if the cluster size is 4 KB or smaller.
NOTE:
To check the cluster size of a volume, use the
fsutil fsinfo ntfsinfo
command. To change the
cluster size on a volume that contains data, back up the data on the volume, reformat it using the new
cluster size, and then restore the data.
HP StorageWorks All-in-One Storage System
145