File Volumes; Directories; Snapshots - HP StorageWorks NAS 8000 - Version 1.6.X Manual

File Volumes

A volume group is divided into one or more file volumes. File volumes are the basic unit of
logical storage for a file system on the NAS 8000. File volumes can be further subdivided into
individual directories.

Directories

Directories let you organize information. Directories contain files or other persistent data
structures in a file system that contains information about other files. Directories are usually
organized hierarchically and may contain both files and other directories, and are used to
organize collections of files for applications or convenience.

Snapshots

A snapshot is a read-only virtual copy of a file volume at a specific point in time. As such, it is
an important part of an overall data-protection plan. Snapshots provide nearly instantaneous
access to previous versions of a file stored on the NAS 8000 solution.
When you create a snapshot of a file volume, it initially consumes no physical space. However,
as users modify the file volume, the snapshot tracks all changes between the original file
volume and the modified file volume. If an error occurs and a user needs to revert to the
previous version, the snapshot version of the file can be restored.
When you create a snapshot, you must allocate storage space in the volume group in which to
save the snapshot file volume. The recommended initial allocation is 10% of the size of the file
volume on which you are using snapshot.
Keep in mind the following when managing your allocated space:
Note:
duplicated in the snapshot. This will require you to allocate a much larger storage space than you
would otherwise need.
Snapshots are optional and may be created at any time after a file volume is created. Users can
add or extend snapshots at a later time if there is enough free space available in the volume
group.
HP StorageWorks NAS 8000 Dedicated Storage High Availability, Solution Integration Manual (SIM)
You can increase the amount of space allocated to the snapshot, as long as there is space
available on the volume group.
If the allocated space fills during a snapshot's existence, you can no longer view or extend
the allocated space. An incomplete snapshot has been captured, and therefore, should be
deleted. The snapshot will be deleted automatically only upon reboot or package failover.
Consider how dynamic your data will be. For file volumes in which data changes rapidly,
snapshots will consume a larger amount of space. At the extreme limit, a file volume can
change so much from the original state that the snapshot consumes the same amount of
space as the original file volume. Typically, data does not change that rapidly, and the
usage and growth of snapshot space is relatively slow.
You may also use the autogrow feature, which allows you to allocate a small amount of
space initially, then instruct the system to increase the size of the allocated space on an
as-needed basis. Ensure that the autogrow threshold is set low enough that it can keep up
with the rate of change in the snapshot files. If the data change rate is greater than the rate
at which the autogrow feature is responding, the allocated space can fill up, thereby
capturing an incomplete snapshot as described above.
If you take a snapshot of an empty file volume, every file added to that volume will be
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