The recommended maximum number of processor cores we state that you should have for a Client Access or Hub Transport server. It’s 12. Memory guidance for Client Access servers is 2 GB per core and for Hub Transport it is 1 GB per core. Thus, if you have a 12-core Client Access server, you’d install 24 GB of memory, and if you had a 12-core Hub Transport server, you would install 12 GB of memory.
Exchange 2010 High Availability and Site Resilience Terminology
But first let’s start with some terminology to make sure everyone understands the components, settings and concepts I’ll be discussing.
| Term | Description | How Configured |
|---|---|---|
| Activation | The process of making a passive database copy into an active database copy. | Move-ActiveMailboxDatabase cmdlet |
| Activation Suspended or Blocked | The process of suspending or blocking a single database or an entire server from automatic activation. | Suspend-MailboxDatabaseCopy or Set-MailboxServer cmdlets |
| Active Manager | An internal Exchange component which runs inside the Microsoft Exchange Replication service that is responsible for failure monitoring and corrective action within a DAG. | N/A |
| Alternate Witness Directory | An optional property of a DAG that specifies the name of the directory that is shared on the Alternate Witness Server for quorum purposes. | Set-DatabaseAvailabilityGroup cmdlet or Exchange Management Console (EMC) |
| Alternate Witness Server | An optional property of a DAG that specifies the witness server that will be used by DAG after you have performed a datacenter switchover. | Set-DatabaseAvailabilityGroup cmdlet or EMC |
| Attempt Copy Last Logs (ACLL) | A process performed during Best Copy Selection in which the system attempts to copy from the original active database copy any log files missing by the passive copy selected for activation. | N/A |
| AutoDatabaseMountDial | Property setting of a Mailbox server that determines whether a passive database copy will automatically mount as the new active copy, based on the number of log files missing by the copy being mounted. | Set-MailboxServer cmdlet |
| Best Copy Selection (BCS) | A process performed by Active Manager to determine the best passive mailbox database copy to activate either in response to a failure affecting the active mailbox database copy, or as a result of an administrator performing a targetless switchover. | N/A |
| Continuous Replication Block Mode | A form of continuous replication that replicates blocks of ESE transaction data between the ESE log buffers on the active mailbox database copy to replication log buffers on one or more passive mailbox databases copies. | N/A – not configurable The system automatically switches between file mode and block mode based on the passive copy’s ability to keep up with continuous replication. |
| Continuous Replication File Mode | A form of continuous replication that replicates closed transaction log files from the active mailbox database copy to one or more passive mailbox database copies. | N/A – not configurable |
| Datacenter | In Exchange, typically this refers to an Active Directory site; however, it can also refer to a physical site. In the context of this blog post, datacenter equals Active Directory site. | N/A |
| Datacenter Activation Coordination (DAC) Mode | A property of the DAG setting that, when enabled, forces starting DAG members to acquire permission in order to mount databases. | Set-DatabaseAvailabilityGroup cmdlet |
| Datacenter Activation Coordination Protocol (DACP) | A bit in memory (0 or 1) that is used by DAG members in DAC mode. A value of 0 indicates the DAG member cannot mount databases; a value of 1 indicates the DAG member can mount active databases that it currently hosts. | N/A – Automatically used when the DAG is configured for DAC mode. |
| Datacenter Switchover | The manual process performed to activate the Exchange components of a standby datacenter and restore Exchange service and data after failure of a primary datacenter. | Process documented in Datacenter Switchovers. |
| Failover | The automatic process performed by the system in response to a failure affecting one or more active mailbox database copies. | N/A – Happens automatically by the system; although you can activation-block or suspend individual mailbox database copies or an entire DAG member. |
| File Share Witness | A cluster-managed resource that is created and use when the cluster uses the node and file share majority quorum model. | N/A – Automatically created and destroyed by Exchange, as needed, based on the number of DAG members. |
| Incremental Resync | A built-in process that corrects certain forms of divergence that occur between mailbox database copies in a DAG (typically between a new active copy and the previous active copy). | N/A – Happens automatically by the system |
| Lossy Failover | A database failover condition in which the passive copy being activated is mounted with one or more log files missing. | Partially controlled via AutoDatabaseMountDial |
| Primary Active Manager (PAM) | An Active Manager role held by a single DAG member at any given time that is responsible for responding to failures an initiating corrective action in the form of a database or server failover. | N/A – The PAM role is automatically held by the DAG member that owns the cluster’s core resource group. |
| Quorum | Has a dual meaning:
| N/A – Automatically configured by Exchange, as needed, based on the number of DAG members. |
| RPCClientAccessServer | A property of a Mailbox database that specifies the Client Access server or Client Access server array through which MAPI/RPC clients (Outlook 2003, Outlook 2007, Outlook 2010) access their mailboxes on that database. | Set-MailboxDatabase cmdlet |
| Site | Active Directory Site, which is defined as one or more fast, reliable and well-connected (< 10 ms latency) subnets. | N/A – Configured outside of Exchange by using Active Directory Sites and Services |
| Split Brain | A condition in which multiple cluster members believe they are authoritative for one or more common resources. | N/A |
| Standby Active Manager (SAM) | An Active Manager role held by all DAG members that do not hold the PAM role that is responsible for monitoring for local failures and responding to queries from CAS and Hub as to the location of the user’s mailbox database. | N/A – The SAM role is automatically held by the DAG members that do not own the cluster’s core resource group. |
| StartedMailboxServers | A list of DAG members that are currently operational and functional. | Automatically added to list during normal operations Manually added to list as part of re-activation of primary datacenter using Start-DatabaseAvailabilityGroup cmdlet |
| StoppedMailboxServers | A list of DAG members that have been marked as non-operational or non-functional. | Automatically added to list during normal operations Manually added to list as part of activation of second datacenter using Stop-DatabaseAvailabilityGroup cmdlet |
| Switchover | In the context of a single database, it is the manual process used to move the active mailbox database copy to another server. In the context of an entire server, it is the manual process used to move all active mailbox database copies from one server to one or more other servers. | Move-ActiveMailboxDatabase cmdlet |
| Targetless Switchover | A switchover process in which the administrator does not specify which passive mailbox database copy should become active, but instead allows Active Manager’s BCS process to choose the best copy to activate. | Move-ActiveMailboxDatabase cmdlet (specifically without using the TargetServer parameter) |
| Transport Dumpster | A feature of the Hub Transport role that retains copies of messages sent to users on replicated mailbox databases in a DAG so that messages can be recovered by the system in the event of a lossy failover of the user’s database. | Set-TransportConfig cmdlet or EMC |
| Witness Directory | A required property of every DAG that specifies the name of the directory that is shared on the Witness Server for quorum purposes. | Set-DatabaseAvailabilityGroup cmdlet or EMC |
| Witness Server | A required property of every DAG that specifies the server external to the DAG that should be used as a participant in quorum for the DAG’s underlying cluster when the DAG contains even number of members. | Set-DatabaseAvailabilityGroup cmdlet or EMC |
