Storage Array Snapshots

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Snapshot

• Snapshot .n
• 1. A logical point-in-time image of another
  volume, called a base volume. A snapshot is the
  logical equivalent of a complete physical copy,
  but you create it much more quickly than a
  physical copy and it requires less disk space.

2
Definitions

• Base n.
• 1. Volume from which the snapshot is created
• Repository n.
• 2. Volume that saves overwritten blocks from
  base volume

3
Why Snapshot

• Reduce backup window to near zero, to
  accommodate 24X7 uptime needs
• Repurposing of on information
• Rapid restore capability
• Application development and test
• Refresh a data warehouse
• Training

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Snapshot Copy
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Snapshot Copy-on Write Process
Write Request
Write Request
Base Volume
S0
S5
S1
S4
S6
S7
S9
S10
S3
S8
S2
Repository
S4
S7
S8
Snapshot Volume
S2
S0
S1
S5
S3
S4
S6
S7
S9
S10
S8
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Reading from a Snapshot Volume
Base Volume
S3
S0
S1
S2
S5
S4
S6
S7
S9
S10
S8
S4
S7
S8
Repository
S1
S0
S5
S2
S4
S6
S7
S9
S10
S8
S3
Snapshot Volume
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Snapshot Volume Attributes
Are Writeable Can be Disabled Can be Recreated
later
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Repository Volume Attributes
Need to consider capacity allocation during
volume creation so as to retain free capacity for
repository volumes Capacity is usually less than
the base volume Small capacity for metadata is
needed Typically it can be expanded later if
needed
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Miscellaneous Points

• Writes to base experience a performance penalty
• Reading a snapshot will be somewhat slower than
  reading a standard volume due to metadata
  operations
• For the release, snapshots can NOT be created
  from another snapshot only a base volume
• Exactly one repository volume is created per
  snapshot
• Formats disallowed on snapshots AND base volumes
• Increasing the capacity of the base volume does
  not change existing snapshots
• When a base volume is delete, all associated
  snapshot volume (And their repositories) are
  deleted along with it a warning is provided in
  the interface.
• When a snapshot is delete, its associated
  repository volume is also deleted -,a warning
  is provided

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Snapshot Flow Chart
Application is up
Unmount Filesystem/Remove Drive Letter
Quiesce Database Hot Backup Mode
Flush disk buffer on host
Perform snapshot
Release Application
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Snapshot User Interface creating a snapshot
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Snapshot User Interface creating a snapshot
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Snapshot User Interface creating a snapshot
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Snapshot User Interface creating a snapshot
15
Snapshot User Interface creating a snapshot
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Snapshot User Interface creating a snapshot
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Snapshot User Interface creating a snapshot