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Recovery Scenarios for E2K7…..II

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This is the second of a few blogs about designing for availability and resilience… The first one is here.

So after understanding what might happen we now need to understand the pro and cons of each component of the proposed solution, the cost associated with each particular component, and the value that it brings to the design.  In other words if a component has a high cost but a low value then let’s not deploy it.

The following table…

Solution Pros Cost Value
Cons  
CCR (Cluster Continuous Replication) Feature of Exchange Server 2007 Replica of data available for fast recovery Mailbox storage requirement is doubled Mailbox server hardware requirement is doubled High – protects against most server failure cases, provides complete replicated data set and rapid failover
2 times server hardware and storage capacity required
SCR (Standby Continuous Replication) Feature of Exchange Server 2007 Replica of data available for fast recovery from data centre failure More storage required More server hardware required Network bandwidth Moderate –very unlikely to be used but provides insurance against the most serious failure case (site loss)
Additional server hardware and storage capacity required Inter-site link required to support replication
DPM (Data Protection Manager) All Exchange data protected Enables fast backups of Exchange data in short term Enables fast recovery of Exchange data in short term Enables long term data retention Provides a last chance to recover when all else fails More storage required More server hardware required Tape devices & media required for long term data retention Moderate – having a recent backup on disk protects against failures not covered by CCR
Replica plus changes stored on disk so more storage required Protection of Exchange data beyond short term retention range is to tape only
Tape Infrastructure All Exchange data protected Enables regular backups of Exchange data to be retained long term Enables long term data retention Tape devices & media required for long term data retention Management and support for a large tape infrastructure Low – keeping data on tape in the long term provides a competing solution to the proposed combination of SCR for site resilience and journal\archive solution for compliance
Reliance on a 3rd party solution Relatively complex and expensive to manage and support
Journaling Feature of Exchange Server 2007 Increase in server hardware requirement on Hub Transport Role Servers and for additional ‘journal’ mailbox role servers Increase in storage requirement for ‘journal’ mailbox role servers Cost of 3rd party archive solution High – a combination of a Journal solution and a 3rd party archive solution ensures that compliance requirements are met
Performance impact on Hub Transport role servers Reliance on a 3rd party archive solution
Deleted Item Retention User led recovery Fast retrieval of email Feature of Outlook client None (For retention periods longer than 14 days mailbox role storage requirements will increase) High
Mailbox role storage must be scaled to allow for long item retention period
Deleted Mailbox Retention Fast administrator led retrieval Feature of Exchange Server 2007 None (For retention periods longer than 30 days mailbox role storage requirements will increase) High
Mailbox role storage must be scaled to allow for long mailbox retention period
Message Tracking Fast administrator led action Feature of Exchange Server 2007 None (For log retention beyond 30 days hub transport role capacity requirements will increase or require a separate storage and search solution) Low-Moderate – keeping recent tracking logs on the server is useful for general troubleshooting in addition to investigating email trails. Retaining more than a month’s worth of tracking logs will require a substantial amount of storage and a solution to make the logs searchable. Again, value is determined by the frequency of search requests
Hub Transport role storage must be scaled to allow for medium term retention of tracking logs Longer term retention of tracking logs must be done off the Exchange server  

So for example the value of protecting data on tape is low but the cost is very high.  In this example solution it would be worth considering not deploying long term protection to tape, or potentially not backing up at all…?

The next blog in this series is called ‘Recovery Scenarios for E2K7…..III’ Once you’ve decided upon a design based on the information compiled in the tables you need to make sure it meets your SLA’s…

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