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The retention period of Snapshots should also be considered. Following is an article from VMWARE on the use of snapshots:

Purpose

This article provides best practice information on using virtual machine snapshots.

Resolution

Follow these best practices when using snapshots in the vSphere environment:

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For long term snapshots of server(s), it is better to copy the entire VMWARE server and then document it (name, purpose, date) and save it off to a storage location.

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Disaster Recovery Plan

Database changes likely occur every second in an MES environment. It is in this area where there is a risk of data loss and RPO tolerance consideration is the most important. Snapshots aren't really an effective means of dealing with recovery from outages which involve rapidly changing transactional data unless they are constantly being taken at short intervals. This is often not practical due to the potential negative impact on the production server of additional load and storage limitations at sites to manage and store all the snapshots.
This traditional backup-and-restore scenario is more suited for databases with lots of real-time transactional data. This can be accomplished by the effective use and planning of Full, Differential, and Transaction Log Backups. One of the main considerations in the strategic deployment of these strategies is the RTO (Recovery Time Objective). A strategy utilizing only a Full Backup and Transaction logs will have a longer RTO than a strategy utilizing a Full Backup followed by Differential backups and transaction logs.

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VMWare Copies

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A full copy of the VMWare server.

Servers	Schedule	Retention
Application	Once every two weeks	One month
Visualization	Once every two weeks	One month
Process Historian	Once every two weeks	One month
SQL Server	Once every two weeks	One month
OPC	Once a month	One month

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Snapshots

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• In the scenarios above the time that it takes to process the recovery of each transaction log is the main factor in the RTO calculation.

• The full backup, differential backup, and transaction logs have to be from the same "set". A previous full backup would not work.

• Regarding data loss and MES data specifically, most transactions that come as a result of process historian data can be "re-triggered" and reprocessed very easily to the same point in time of the disaster. The transactions that are at risk to be missed are any transactions that were manually entered by operators or downloaded from 3^rd party applications via interfaces.

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SQL AGENT Database Backup

An SQLAgent job can be set up to perform Maintenance jobs to perform Database and transaction log backups.
For example, you might schedule three jobs: Full Backup, once per day, a Differential, every 12 hours, and Transaction Log backup every 15 minutes or half-hour. Database and Transaction Log backups would then be sent to an offline storage device like a NAS server.

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Historian Archives and OPC Project Configuration Files

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