Adaptec 5325301638 - Snap Server 4500 NAS, Administrator'S Manual

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Estimating Snapshot Pool Requirements
Chapter 7 Snapshots 57
Estimating Snapshot Pool Requirements
Snapshot data grows dynamically for as long as a snapshot is active and as long as
there is enough space available in the snapshot pool to store them. When the
snapshot pool approaches its capacity (at about 95 percent), the Snap Server deletes
the oldest snapshot’s data to create space for more recent snapshot data.
The default configuration allocates 80 percent of RAID capacity to the volume and
20 percent to the snapshot pool. You can adjust the size of the pool up (assuming
unallocated space exists) or down according to your needs. If you find that your
snapshot strategy does not require all of the space allocated to the snapshot pool by
default, consider decreasing snapshot pool capacity and re-allocating the capacity
to the file system. To adjust the size of the snapshot pool, navigate to the
Storage >
Snapshots
screen, and click the
Adjust Snapshot Space
link in the introductory text.
The number of snapshots that a RAID can support is a function of these factors: (1)
the space reserved for the snapshot data; (2) the duration of the snapshots you
create; and (3) the amount and type of write activity to the volume(s) since the
snapshot was created. The following table describes minimum and maximum
allocation cases.
Adjusting Snapshot Pool Size
The current size of the snapshot pool for each RAID (or RAID group) can be viewed
by navigating to the
Storage > Snapshots
screen and clicking the
adjust snapshot
space
link in the introductory text. On the screen that opens, you can adjust the pool
up or down as necessary at any time. In addition, there are two other processes that
may affect the size of the snapshot pool.
• Creating a Volume —
In the course of creating a new volume, a pull-down menu
allows you to add a percentage of the capacity being allocated to the new volume
to the snapshot pool. This feature defaults to 20%, the recommended amount of
space to reserve for snapshots. If you do not plan to use snapshots with this
volume, maximize volume capacity by reducing this percentage to zero; if you do
plan to use snapshots, adjust this percentage in accordance with the guidelines
discussed in previous section.
Guidelines for Estimating Snapshot Pool Requirements
Allocate about 10% of RAID if Allocate about 25% of RAID if
• Activity is write-light
• Write access patterns are concentrated in
a few places
• A small number of Snapshots must be
available at any point in time
• Activity is write-heavy
• Write access patterns are randomized
across the volume
• A large number of Snapshots must be
available at any point in time