High Availability is nothing but a pre-solutions back up where we are keeping our system accessible to users. i.e keeping the servers up as much as possible it not only include that servers should not goes down but also include the performance so that all users can access the resource without any issue.
Examples include…
- Clustering
- Load balanced hosts
- Built-in redundancy or load balancing
- DNS / application redundancy or load balancing
Solutions that allow for contingency of operations
- Recovery in the event of a serious disaster
- Usually not automatic failover
- Examples include…
- Standby Continuous Replication
- Local Continuous Replication
High Availability for E2K7
- High Availability for Mailbox Server
- High Availability for Client Access Server
- High Availability for Hub Transport Server
- High Availability for Edge Transport Server
- High Availability for Unified Messaging
High Availability for MBX
High availability for Mailbox servers comes in two forms: service availability and data availability.
Service availability is provided through the use of a Windows Server failover cluster. Data availability is provided through a built-in feature called continuous replication.
Continuous Replication
- Continuous replication, also known as log shipping, is the process of automating the replication of closed transaction log files from a production storage group to a copy of that storage group that is located on a second set of disks on the local computer or on another server altogether. After being copied to the second location, the log files are then replayed into the copy of the database, thereby keeping the storage groups synchronized with a slight time lag.
- Continuous replication is available in two forms in Exchange 2007 RTM (LCR and CCR) and three forms in Exchange 2007 SP1 (LCR, CCR, and SCR).
- Apart from Continuous Replication we have another form of availability called as SCC
Local Continuous Replication
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
Cluster Continuous Replication
CCR, which is a non-shared storage failover cluster solution, is one of two types of clustered mailbox server (CMS) deployments available in Exchange 2007. CCR is a clustered solution (referred to as a CCR environment) that uses built-in asynchronous log shipping technology to create and maintain a copy of each storage group on a second server in a failover cluster. CCR is designed to be either a one or two data center solution, providing both high availability and site resilience.
Standby Continuous Replication
- Coming in Service Pack 1
- Source and target machines can be
- Stand-alone
- In two different MSCS clusters
- On different subnets
- Controlled per storage group
- Many-to-one and one-to-many supported
- Manually activated
LCR Vs CCR Vs SCR
- LCR
- –Focused towards resiliency
- –Improve restore time
- –Administrator has to initiate restore manually
- –Single data-center solution
- –Implements log shipping and replay out of the box
- Log files are copied locally and replayed
- CCR
- Targeted towards site resiliency
- Automatic failovers
- Single or two-data center solution
- Supports “stretch” option
- Implements log shipping and replay out of the box
- Log files are copied to remote server and replayed
- Simplifies cluster deployment
- No SAN or shared storage
- SCR
- Provides site and server resiliency
- “Cold spare” approach cuts hardware costs
- Can be combined with LCR, CCR, and SCC for maximum flexibility
Single Copy Cluster
SCC, which is a shared storage failover cluster solution, is the other of two types of clustered mailbox server deployments available in Exchange 2007. 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 somewhat similar to clustering in previous versions of Exchange Server; however, along with numerous improvements, there are also some significant changes.
Other Mode of Clusters
- Stretch Cluster
A stretch cluster, also known as a geographically dispersed cluster, is a failover cluster that is stretched (that is, it spans) more than one physical datacenter. Stretch clusters can be used as part of a site resilience design for your Exchange organization. Because CCR does not use shared storage, it can be easily deployed in a geographically dispersed failover cluster, including a multi-subnet stretch cluster on Windows Server 2008. SCC is also supported in a stretch cluster; however, stretching SCC requires third-party synchronous replication technology.
- Standby Cluster
Another type of cluster that is supported by Exchange 2007 and Exchange 2007 SP1 is called a standby cluster. A standby cluster is a Windows Server failover cluster that does not contain a clustered mailbox server, but can be quickly provisioned with a replacement clustered mailbox server in the event of a disaster, another failure of the production failover cluster, or some other recovery scenario.
HA for other Server Roles
- Edge Transport You can deploy multiple Edge Transport servers and use multiple DNS Mail Exchanger (MX) records to load balance activity across those servers.
- Client Access You can use NLB or a third-party hardware-based network load-balancing device for Client Access server high availability.
- Unified Messaging 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 Voice over IP (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.
- Hub Transport You can deploy multiple Hub Transport servers for internal transport high availability. Resiliency has been designed into the Hub Transport server role in the following ways:
- Hub Transport server to Hub Transport server (intra-org) Hub Transport server to Hub Transport server communication inside an organization automatically load balances between available Hub Transport servers in the target Active Directory directory service site.
- –Mailbox server to Hub Transport server (intra-Active Directory site) The Microsoft Exchange Mail Submission service on Mailbox servers automatically load balances between all available Hub Transport servers in the same Active Directory site.
- –Unified Messaging server to Hub Transport server The Unified Messaging server automatically load balances connections between all available Hub Transport servers in the same Active Directory site.
- –Edge Transport server to Hub Transport server The Edge Transport server automatically load balances inbound Simple Mail Transfer Protocol (SMTP) traffic to all Hub Transport servers in the Active Directory site to which the Edge Transport server is subscribed.
How to check ClusterMBX type
You can also check Active Directory to determine if a clustered mailbox server is hosted in a CCR environment or in an SCC by examining the value for the msExchClusterStorageType attribute of the Mailbox server object. A value of 1 for the msExchClusterStorageType attribute indicates that the clustered mailbox server is hosted in a CCR environment, and a value of 2 indicates that the clustered mailbox server is in an SCC. A value of <Not Set> indicates that the Mailbox server is a stand-alone server.
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