Estimating Snapshot Pool Requirements
Chapter 7 Snapshots
113
Snapshots and iSCSI Disks
Running a GuardianOS snapshot on a volume containing an iSCSI Disk will
abruptly disconnect any clients attempting to write to the iSCSI Disk and the
resulting snapshot may contain inconsistent data. Do not use GuardianOS
snapshots on a volume containing an iSCSI Disk.
To create a native snapshot of an iSCSI disk on Windows systems, use the VSS
feature described in “Configuring VSS/VDS for iSCSI Disks” on page 93.
Estimating Snapshot Pool Requirements
Snapshot data grow 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 SnapServer 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 reallocating the capacity to
the file system. To adjust the size of the snapshot pool, navigate to the
Storage >
Snapshots
screen, click the
Snapshot Space
button, then click the Raid Set for the
snapshot pool you want to adjust.
The number of snapshots that a RAID can support is a function of these factors:
• The space reserved for the snapshot data
• The duration of the snapshots you create
• 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.
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
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