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High Availability

High Availability

This part includes all the information about High Availability options  introduced in Exchange Server 2007.

please, Leave your comments on this….

1. What is high availability in Exchange Server 2007?

The basic premise of the Exchange 2007 high availability architecture is to introduce redundancy into the deployment. A failure is recovered using the remaining computing resources to support the Exchange services. As the failures are repaired, computing resources are again available to Exchange and its clients. In this context, the computing resources may be computers or storage for mailbox or other Exchange data.

2. What are the uses of high availability features available in Exchange Server 2007?

Microsoft Exchange Server 2007 includes built-in features that can provide quick recovery, high availability, and site resiliency for Exchange Server 2007 Mailbox servers.

3. What are the high availability features available in Exchange Server 2007 for Mailbox server role?

  1. Local continuous replication
  2. Cluster Continues Replication
  3. Standby Continuous Replication
  4. Single Copy Cluster

4. What is LCR?

LCR is a single-server solution that uses built-in asynchronous log shipping technology to create and maintain a copy of a storage group on a second set of disks that are connected to the same server as the production storage group. LCR provides log shipping, log replay, and a quick manual switch to a secondary copy of the data.

5. What do you know about LCR?

  1. Provides data redundancy without service redundancy·
  2. Partition data for performance and recovery·
  3. Ensure sufficient disk space,
  4. CPU and memory resources should be considered

6. What is SCR?

SCR is a new feature introduced in Exchange 2007 SP1. As its name implies, SCR is designed for scenarios that use or enable the use of standby recovery servers. SCR extends the existing continuous replication features and enables new data availability scenarios for Exchange 2007 Mailbox servers. SCR uses the same log shipping and replay technology used by LCR and CCR to provide added deployment options and configurations. SCR can be used to replicate data from stand-alone Mailbox servers and clustered mailbox servers.

7. What is the function of source server in SCR?

The starting point for SCR is called the source, which is any storage group on any of the following:

  • A stand-alone Mailbox server
  • A clustered mailbox server in a single copy cluster (SCC)
  • A clustered mailbox server in a CCR environment

As with LCR and CCR, SCR-enabled storage groups cannot contain more than one database. You cannot enable SCR for a storage group that contains more than one database, and you cannot add a second or subsequent database to an SCR-enabled storage group

SCR Source Server holds the active copy of Mailbox database

8. What is the function of Target Server in SCR?

The endpoint for SCR is called the target, and the target can be either of the following:

  • A stand-alone Mailbox server that does not have LCR enabled for any storage group
  • A passive node in a failover cluster where the Mailbox role is installed, but no clustered mailbox server has been installed in the cluster

An SCR target computer must have the Mailbox server role installed, even if it does not host production mailboxes. The Mailbox server role is required because it includes the Microsoft Exchange Replication Service and other components necessary for SCR functionality

The Target Server holds the passive copy of Mailbox database

  1. What are the conditions to have target Server?

The Target server may be,

A stand-alone Mailbox server that does not have LCR enabled for any storage group

A passive node in a failover cluster where the Mailbox role is installed, but no clustered mailbox server has been installed in the cluster

10. Explain the functionality of SCR?

SCR is designed for scenarios that use or enable the use of standby recovery servers. SCR extends the existing continuous replication features found in the release to manufacturing (RTM) version of Exchange Server 2007 and enables new data availability scenarios for Mailbox servers running SP1. SCR uses the same log shipping and replay technology used by local continuous replication (LCR) and cluster continuous replication (CCR) to provide added deployment options and configurations

11. What is CCR?

CCR is a clustered solution that uses built-in asynchronous log shipping technology to create and maintain a storage group copy on a second server. CCR is designed to be either a one or two datacenter solution, providing both high availability and site resilience.

12. What is Witness File Share?

It is a new type of Majority Node Set (MNS) quorum in Windows Server 2003. In Exchange Server 2007, cluster continuous replication (CCR) uses the MNS quorum with file share witness instead of the traditional voter node.

This feature lets you use a file share that is external to the cluster as an additional vote to determine the status of the cluster in a two-node MNS quorum cluster deployment.

The file share witness uses a file share on a computer outside the cluster to act as a witness to the activities of the two nodes that are the cluster. The witness is used by the two nodes to track which node is in control of the cluster. The note board is only required when the two nodes cannot communicate with each other

13. What are the advantages of CCR over LCR?

  • Has no single point of failure.
  • Has no special hardware requirements
  • Has no shared storage requirements
  • Can be deployed in one or two datacenter configurations
  • Can reduce full backup frequency, reduce total backed up data volume, and shorten the service level agreement (SLA) for recovery time from first failure.

14. What is SCC?

SCC is a clustered solution that uses a single copy of a storage group on storage that is shared between the nodes in the cluster. SCC is very similar to clustering in previous versions of Exchange Server, with some significant changes and improvements

15. Explain the high availability options for client Access Server Role?

You can use Network Load Balancing or a third-party hardware-based network load-balancing device for Client Access server high availability. For more information about Network Load Balancing

16. Explain the high availability options for Hub Transport Server Role?

You can deploy multiple Hub Transport servers for internal transport high availability. Resiliency has been designed into the Hub Transport, as well as the Mail Submission Service on Mailbox servers, for deployment of multiple Hub Transport servers. In Exchange 2007 SP1, you can also use NLB for the client connectors on Hub Transport servers.

17. Explain the high availability options for Edge Transport Server Role?

You can deploy multiple Edge Transport servers and use multiple DNS Mail Exchanger (MX) records to load balance activity across those servers

18. Explain the high availability options for Unified Messaging Server Role?

Unified Messaging deployments can be made more resilient by deploying multiple Unified Messaging servers where two or more are in a single dial plan. The VoIP gateways supported by Unified Messaging can be configured to route calls to Unified Messaging servers in a round-robin fashion. In addition these gateways can retrieve the list of servers for a dial plan from DNS. In either case, the VOIP gateways will present a call to a Unified Messaging server and if the call is not accepted, the call will be presented to another server, providing redundancy at the time the call is established.

19. What the requirements to configure SCR?

SCR allows an Exchange Admin to replicate a copy of Storage Group to a number of remote servers. Microsoft recommends a max of 4 target machines.

An SCR Source can be an LCR, CCR, SCC, or Stand alone mailbox server but requires only 1 Database per Storage Group which is already a requirement for LCR and CCR.

The target can be on the same subnet or in a remote datacenter unlike CCR which currently requires both nodes be on the same subnet

1. The paths must be the same for both machines
– If source server is c:\Server1\Data and C:\Server1\Logs then these paths must be available on the target server.

2. There is a hard coded 50 log lag between the Source and Target
– by default there is a 24 hour replay time which is configurable.

3. There can be only 1 database per storage group

4. The target server must have Exchange mailbox role installed, if this is a cluster it will be install as a passive node.

5. The target server must be in the same Active Directory domain

  1. What are the requirements to configure LCR?

LCR does not have any special storage requirements. Any type of storage that is supported by Windows Server 2003 or Windows Server 2008 can be used with LCR, including direct attached storage, serially attached SCSI, and Internet SCSI (iSCSI)

21. What the requirements to configure CCR?

To setup a CCR-based cluster, the following are required

Software Requirements

  • Windows 2003 Active Directory forest with at least one domain controller raised to windows 2003 forest functional level
  • Two windows 2003 server R2 Enterprise Edition or windows server 2003 sp1 standard or enterprise edition
  • One windows file share witness, which is recommended to be an exchange 2007 Hub transport Server in the existing Exchange organization; note the CCR-based cluster don’t use a shared quorum as traditional clusters do
  • A cluster Service account in the Active directory forest

Hardware requirements

  • Two NIC installed in each node, one for the public and one for the private cluster network
  • Extra sets of disks or a DAS, SAN or Serial SCSI solution to hold the database and transactional log files

Other Requirements

  • Only one database per storage group
  • You cannot create public folder database in a CCR environment if you already have one
  • Microsoft recommends the no more 30 storage groups and databases on clustered mailbox server
  • The cluster on which Exchange Server 2007 is installed cannot contain Exchange Server 2000/2003 or any version of MS SQL server. Running Exchange Server 2007 in a cluster with any of these other application is simply not supported

22. What the requirements to configure SCC?

Windows 2003 Active Directory forest with at least one domain controller raised to windows 2003 forest functional level

Two windows 2003 server R2 Enterprise Edition or windows server 2003 sp1 standard or enterprise edition

At least one existing HT server, which is recommended to be an exchange 2007 Hub transport Server in the existing Exchange organization

Two machine with two NICS to create a Public and private network

23. Compare SCR with LCR and CCR?

SCR supports multiple replication targets per storage group. LCR and CCR support only one replication target per storage group (the passive copy).

SCR includes a built-in delay for replay activity, and it enables an administrator to specify an additional delay. This is useful in a variety of scenarios. For example, in the event of logical corruption of an active database, the built-in and additional administrator-configured delay could be used to prevent logical corruption of an SCR target database. LCR and CCR have no such delays.

SCR is completely managed using the Exchange Management Shell. The Exchange Management Console can be used to manage many aspects of LCR and CCR, but it cannot be used to enable or manage any aspects of SCR

You cannot back up an SCR target copy. LCR and CCR support backups from both the active and passive copy. SCR supports backups of the SCR source only

24. What is Replaylagtime and TruncationLagTime?

Replaylagtime – Time that the Microsoft Exchange Replication Service should wait before replaying logs. Default is 24 hours and max time is 7 days.

TruncationLagTime – Amount of time Microsoft Exchange Replication Service waits before truncating log files that have been copied to the target

25. What is seeding?

Seeding is the process whereby a database is added to a storage group copy, this can be a blank database or a copy of the database the storage group uses as the production database. When you enable the LCR on a storage group using the EMC, seeding normally takes place automatically.

26. Will seeding happens automatically? Then why should we care about it?

Seeding normally takes place automatically, in some situations manual seeding is required.

  • After you have performed an offline defragmentation of the production database belonging to the storage group for which you have enabled LCR
  • When exchange detects corrupted log, which the Microsoft Exchange Replication Service cannot replay into the database copy
  • After a page scrubbing of a database on the active node in a CCR setup occurs, and you want to propagate these seeding

27. Explain the LCR operation?

The database type Exchange uses is Extensible Storage Engine (ESE). ESE employs transactional log files, which means that every time a modification is made, a transactional log file is generated (instead of the change being committed directly to database). This process is to make exchange always able to recover the lost data, which is in memory by using log files.

Each log file that is generated because of a modification in the database belonging to the active copy of the Storage is replicated from the source log folder to the target log folder associated with the passive copy of the storage group. This is not the entire truth, because each log file is first copied to an inspector log folder located beneath the target folder, where it is inspected to make sure it is correct. If it is not correct it will be re copied. Finally the file is copied to the target log folder and from there replayed into the database belonging to the passive copy of the Storage Group

A new Exchange Server 2007 service called the Microsoft Exchange Replication Service will be installed on any Exchange Server 2007 servers with the mailbox server role installed. These are responsible for replicating the log files to the target log folder

28. What is suspending in LCR? And how to achieve it?

Suspending LCR means that all log file shipping as well as log file replaying is halted.

Suspending LCR is a straight forward process, it is done by selected the respective Storage group in the EMC, and then clicking the Suspend Local Continuous replication in the Action pane.

29. What is log file shipping and log file replaying?

Log File Shipping

Log shipping allows you to automatically send transaction log backups from a primary database on a primary server instance to one or more secondary databases on separate secondary server instances. The transaction log backups are applied to each of the secondary databases individually. An optional third server instance, known as the monitor server, records the history and status of backup and restores operations and, optionally, raises alerts if these operations fail to occur as scheduled.

Log shipping consists of three operations:

1. Back up the transaction log at the primary server instance.

2. Copy the transaction log file to the secondary server instance.

3. Restore the log backup on the secondary server instance.

Log file replay

The transactional logs are generated on the active node are replicated to the information store on the passive node using log file shipping. These replicated log files are then posted into the databases on the passive node using the log file replay technology, this means that should the active node or a database on this node fails or for some other reason go offline, an automatic failover to the passive node will occur. Hence the passive node becomes the active node, the replication of log file will happen from the new active node to passive node.

30. Explain the CCR operation?

With CCR, the transactional logs are generated on the active node are replicated to the information store on the passive node using log file shipping. These replicated log files are then posted into the databases on the passive node using the log file replay technology, this means that should the active node or a database on this node fails or for some other reason go offline, an automatic failover to the passive node will occur. Hence the passive node becomes the active node, the replication of log file will happen from the new active node to passive node.

31. Explain the SCC operation?

SCC is more or less identical to the traditional active/passive clusters we know from the previous version of Exchange. This means that a SCC-based cluster only provides service failover and still has a single point of failure when it comes to databases, unless a shared storage solution that provides redundancy in other means is used in the environment. An SCC cluster using fault tolerant SAN is much more expensive than a CCR solution

An SCC is basically a clustered mailbox server that consists of two or more servers that share the same storage for database and log files. The shared storage subsystem is basically a SAN

32. What is the advantage of CCR over SCC?

Deploying CCR instead of SCC has several advantages,

  • you no longer have a single point of failure regarding database
  • Unlike SCC, CCR doesn’t require a shared storage subsystem such as SAN, because the nodes in a CCR don’t share the same disk
  • You have the option of spanning the CCR between two locations

33. How many databases can I have in each storage group when I’m using either LCR or CCR?

You can only have one database in each storage group when using either LCR or CCR. In addition, you cannot have more than one Public Folder database in the organization if you want to replicate a public folder database using CCR technology

34. Explain LCR, CCR and SCR in short?

LCR requires that database replicas are stored locally; CCR lets you store database replicas on a different server that must exist in the same subnet as the primary database server. With this, you can have only one replica.

SCR allows your primary mailbox server (source) to replicate its database to multiple standby servers (targets). These target servers can exist on your LAN, but that isn’t necessary. The subnet limitation doesn’t apply to SCR.

35. What is a Standby Cluster?

A standby cluster is a Windows cluster that matches a production Exchange cluster in terms of hardware and software configuration, including Windows and Exchange versions and any updates or hot fixes that have been applied. In addition, a standby cluster has the Exchange program files installed but has not yet been configured with any Exchange Virtual Servers (EVS). Lastly, a standby cluster can only be used when all Exchange Virtual Servers on the production cluster are offline.

36. Will the standby cluster works with Exchange Server 2007?

The answer is no, but then it’s really not that useful anymore, since Exchange 2007 gives us the ability to recover an Exchange 2007 cluster using the new Exsetup/RecoverCMS switch (which is similar to the /DisasterRecovery switch we know from previous versions of Exchange).

 

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