VNX Block Local Replication Principles
Upon completion of this module, you should be able to:
• Explain the business cases for VNX block local replication
• List VNX SnapView and VNX Snapshot basic terminology
• Explain operating principles for the following:
 VNX SnapView
 VNX Snapshot
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VNX Block Local Replication Principles
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VNX Block Local Replication Business Cases
• Primary goals
 Creation of point-in-time copies of data
 Support for consistent on-line backup or data replication
 Offload backup and other processing from production hosts
• Data copies can be used for purposes other than backup
 Testing, decision support scenarios, local data migration
• A successful recovery requires that consistent data was written
•
•
to the backup media
SnapView supports consistency for Snapshots and clones
VNX Snapshots support Consistency Groups
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VNX Block Local Replication Principles
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SnapView Overview
• SnapView Snapshots
 Use pointer-based replication and Copy on First Write technology
 Make use of a Reserved LUN Pool to save data chunks
 Have three managed objects: Snapshot, Session, Reserved LUN Pool
• SnapView Clones
 Make full copies of the Source LUN (Classic, Thick , or Thin)
 Track changes to Source LUN and Clones in the Fracture Log
 Have three managed objects: Clone Group, Clone, Clone Private LUN
• SnapView Snapshots and SnapView Clones are managed by
 Unisphere
 Navisphere Secure CLI
 Admsnap
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VNX Block Local Replication Principles
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SnapView Terminology
Term
Definition
Production host
Server where customer applications are executed
Source LUNs are accessed from the production host
Backup (secondary)
host
Host where backup processing occurs
Offloads backup processing from production host
Snapshots and clones are accessed from backup host
Admsnap utility
An executable program that runs interactively or with a script to manage
clones and snapshots
Resides on the servers connected to the storage system
Source LUN
Production LUN – the LUN from which replicas are made
Activate
Maps a snapshot to an available snapshot session
Snapshot
A point-in-time copy of a Source LUN
Reserved LUN Pool
(RLP)
Private area used to contain Copy on First Write (CoFW) data
Total number of Reserved LUNs is limited
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VNX Block Local Replication Principles
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SnapView Terminology (continued)
Term
Definition
Snapshot session
Defines a point-in-time designation by invoking CoFW activity for updates
to the Source LUN
Snapshot session
name
Name for a session that is used for subsequent operations (sessions should
have meaningful names)
Chunk
Granularity at which data is copied from the Source LUN to a reserved area
Copy on First Write
(CoFW)
When a chunk is changed on the Source LUN for the first time, data is
copied to a reserved area
Fracture
The process of breaking off a clone from its source
Once a clone is fractured, it can receive server I/O requests
Clone group
Contains a Source LUN and all of its clones
Clone private LUNs
Used for recording information that have been modified on the Source LUN
and clone LUN that has been fractured
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VNX Block Local Replication Principles
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SnapView Features
• SnapView enabler allows use of Snapshots and Clones
• Snapshots and Clones have high availability features
 Resilient to SP and path failures (if PowerPath is installed), LUN
trespasses, and non-disruptive upgrades
• Multiple point-in-time copies allowed
• Restore to Source LUN capability
 Primary host sees changes immediately
 Minimal disruption to production data processing
• Consistency of data across multiple objects
 Consistent session start, consistent clone fracture
• Simplified management with wizards
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VNX Block Local Replication Principles
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SnapView Technologies Comparison
• Access to point-in-time copy
 Snapshot data is immediately available for use
 Clones need an initial full synchronization, which is time-consuming
• Performance impact on Source LUN
 Snapshots use Copy on First Write, which increases response times
 Fractured Clones are independent of their Source LUNs
• Use of disk space
 A Snapshot uses around 20% of the space of its Source LUN
 A Clone occupies the same amount of space as its Source LUN
• Recovery from Source LUN loss or corruption
 Snapshots depend on a Source LUN for operation
 Clones can be completely independent of the Source LUN
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VNX Block Local Replication Principles
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SnapView Snapshot Limits
Parameters
VNX5400
VNX5100
VNX5600
VNX5300
VNX5800
VNX5500
VNX7600
VNX5700
VNX8000
VNX7500
Max SnapView
Snapshots per
storage system
256
512
512
1024
2048
Snapshots per
source LUN
8
8
8
8
8
Max SnapView
Snapshot sessions
per source LUN
8
8
8
8
8
Reserved LUNs per
storage system
128
256
256
512
512
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VNX Block Local Replication Principles
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SnapView Clone Limits
Parameters
VNX5400
VNX5600
VNX5800
VNX7600
VNX8000
SnapView Clones per
storage system
256
1024
2048
2048
2048
SnapView Clones per
source LUN
8
8
8
8
8
128
256
1024
1024
1024
2
2
2
2
2
Parameters
VNX5100
VNX5300
VNX5500
VNX5700
VNX7500
SnapView Clones per
storage system
128
256
512
1024
2048
SnapView Clones per
source LUN
8
8
8
8
8
64
128
256
512
1024
2
2
2
2
2
Clone groups per
storage system
Clone private LUNs
per storage system
Clone groups per
storage system
Clone private LUNs
per storage system
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VNX Block Local Replication Principles
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VNX Snapshot Overview
• VNX Snapshots
 Use pointer-based replication and Relocate on First Write (ROW)
technology
 Make use of the source LUN’s parent Pool to store original data
 Have three managed objects: Snapshot, Snapshot Mount Point,
Consistency Group
• VNX Snapshots are managed by
 Unisphere
 Navisphere Secure CLI
 Unisphere SnapCLI
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VNX Block Local Replication Principles
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VNX Snapshot Terminology
Term
Definition
Primary LUN
Production LUN – the LUN from which replicas are made
VNX Snapshot
A point-in-time replica of a Primary LUN
Attach
Maps a snapshot to a Snapshot Mount Point (SMP)
Detach
Removes the mapping between a snapshot and a Snapshot Mount Point
Restore
Restore the Primary LUN to a point in time copy
Unisphere SnapCLI utility
An executable program that runs interactively or with a script to manage VNX
Snapshots
Snapshot Mount Point
(SMP)
Virtual LUN which can be attached to a VNX Snapshot to make it visible to a host
Consistency Group
Persistent grouping of primary LUNs or Snapshot Mount Points
Snapshot family
Pool LUN, all of its associated mount points, and all of their snapshots
Relocate on First Write
(ROW)
When data is changed on the Primary LUN for the first time, data is written to another
area in the Pool
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VNX Block Local Replication Principles
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VNX Snapshot Features
• VNX Snapshot enabler allows use of VNX Snapshots
• Multiple point-in-time copies allowed
• Restore to Primary LUN capability
 Primary host sees changes immediately
 Minimal disruption to production data processing
• Consistency of data across multiple objects
 Consistency groups
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VNX Block Local Replication Principles
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VNX Snapshot Limits
Parameters
VNX5400
VNX5600
VNX5800
VNX7600
VNX8000
VNX Snapshots per
storage system
8000
8000
16000
24000
32000
VNX Snapshots per
primary LUN
256
256
256
256
256
VNX Snapshots per
Consistency Group
64
64
64
64
64
Consistency Group
per storage system
128
128
128
256
256
1000
1000
2000
3000
4000
128
128
256
512
512
VNX Snapshot Mount
Points per storage
system
Concurrent Restore
Operations per
storage system
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VNX Block Local Replication Principles
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VNX Snapshot and SnapView Snapshot
Comparison
VNX Snapshot Term
SnapView Snapshots
Term
Definition
Snapshot
Session
Point in time copy
Restore
Rollback
Restore primary LUN to point in
time copy
Attach
Activate
Make the point in time copy
accessible to a host
Detach
Deactivate
Remove the point in time copy
from the host
Consistency Group
n/a
Persistent grouping of primary
LUNs or Mount Points
Snapshot Family
n/a
Pool LUN, all of its associated
mount points and all of their
snapshots
Primary LUN
Source LUN
Pool LUN that can be used by
VNX Snapshots
Snapshot Mount Point
Snapshot [LUN]
LUN that host uses to access the
snapshot data
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VNX Block Local Replication Principles
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VNX Snapshot and SnapView Snapshot Features
Feature
VNX Snapshots
SnapView Snapshots
Snapshot Space
Automatic in same pool
Reserved LUN Pool
Max Snapshots per source
256
8
Max Snapshots per array
32,768
2048
Snapshots of Snapshots
Yes
No
Consistent Snapshots
Yes
Yes
Consistency Groups
Yes
No
Automatic Snapshot space
management
Auto-Delete snapshots &
Snapshot expiration
None
Auto Naming
Optional
No
Source LUN type
Pool LUNs, Consistency Groups, and
Snapshot Mount Points
All LUNs
Snapshot Description
Yes
No
Restore/Rollback
Yes
Yes
In-Band Snapshot management
Yes
Yes
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VNX Block Local Replication Principles
15
Summary
Key points covered in this module:
• VNX block local replication business cases
• VNX SnapView and VNX Snapshot basic terminology
• VNX SnapView Snapshot operating principles
• VNX Snapshot operating principles
• VNX SnapView Clone operating principles
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VNX Block Local Replication Principles
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