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Chapter 4
LUN Configuration
When a Snapshot is created, its initial size is automatically calculated based upon the size of the
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Origin LUN.
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Snapshots are automatically resized based upon the number of changes to the Origin LUN and the
amount of free space left on the Origin LUN. Depending on the rate of change on the origin, the
snapshot may occasionally resize to become larger than the Origin LUN.
Snapshots can be mounted for read/write purposes.
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One or more Snapshots can be deleted manually. Note that an Origin LUN cannot be deleted unless
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all of its snapshots are deleted beforehand. To that extent, you cannot select to delete both the Origin
LUN and the Snapshot together.
When available free space on the system falls below a threshold level of 10%, the system
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automatically deletes the oldest Snapshot on the device to free up space.
A LUN Snapshot can be merged (only) with its Origin LUN, one Snapshot at a time, without concern
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about the order in which the Snapshots were created.
Snapshot performance under I/O can be checked.
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Snapshot scheduling applies to the current SSR only and is not accessible from other SSRs. If the
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current SSR is down, the configured Snapshot schedule is not executed during this downtime from
other SSRs.
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When available free space on the system falls below a threshold level of 10% scheduled or manual
Snapshot creation is not permitted. To create space, the system automatically deletes the oldest
Snapshot(s) until there is at least 15% of free space on the device.
A LUN Snapshot can be merged (only) with its Origin LUN, one Snapshot at a time, without concern
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about the order in which the Snapshots were created.
If the Snapshot becomes degraded for any reason (i.e., it is consistently displayed in red on the LUN
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list), call the Cisco Technical Support for assistance as it is not possible to delete this Snapshot from
the user interface.
Snapshots cannot be used either as a Source or Destination for creating an Async Replication
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pairing.
Increasing the size of LUNs containing Snapshot(s) is not permitted. You must delete all the
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snapshots for the Origin LUN Snapshot prior to increasing its size.
You should regularly monitor the growth of the Snapshot and the amount of disk space available on the
Caution
device.
If there is not enough free space for a Snapshot's automatic resize, the Snapshot may become invalid and
may no longer track changes on the Origin LUN. In addition, any mounted file systems on that Snapshot
device may be forcibly unmounted.
Note
The following three conditions must be true for the successful operation of the Snapshot feature:
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The maximum number of Snapshots PER SSR is limited to 254.
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The total number of Snapshots per hour for the entire device (both SSRs) is less than 20.
Each LUN is scheduled at a maximum rate of one Snapshot per hour.
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Cisco UCS Invicta Scaling System Administration and Configuration Guide, Version 5.0.1.1a
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