Microsoft Exchange Server 2010: High Availability Deep Dive (including changes introduced by SP1)

Important in Exchange HA is Quorum so we will start here:

Quorum

Dual Usage of Quorum:

  • Data shared between the voters representing configuration, etc.
    • Physical data located on DAG servers.
  • Number of voters required for the solution to stay running (majority).

Exchange 2010 uses only two of four available cluster quorums

  • Node majority
  • Node and file share Majority

It is essential for function in the DAG.

Witness

A witness is a file share on a server (witness server).

Needed for quorum decisions

                             One of the nodes will lock witness.log referred as the locking node.

Only used by DAGs that have a even number of members (node and file share majority quorum mode)

Witness server

No pre-configuration typically necessary

  • Exchange Trusted Subsystem must be member of local Administrators group on Witness Server if Witness Server is not running Exchange 2010

Must be in the same Active Directory forest as DAG

Can be Windows Server 2003 or later

  • File and Printer sharing for Microsoft Networks must be enabled

Replicating witness directory/share with DFS not supported

Not necessary to cluster Witness Server

  • If you do cluster witness server, you must use Windows 2008

Single witness server can be used for multiple DAGs

  • Each DAG requires its own unique directory/share

 DAG networks

Used for multi Subnet DAG

A DAG network is a collection of subnets

There a two types of DAG Networks:

  • MAPI Network – Connects DAG members to network resources (Active Directory, other Exchange server, DNS) Default GW will be configured here
  • Replication Network – Used for/by continuous replication only (log shipping and seeding)

DAG Networks automatically created when Mailbox server is added to DAG

DAG Networks include built-in encryption and compression

  • Encryption: Kerberos SSP EncrypsMEssage/DecryptMessage APIs
  • Compression: Microsoft XPRESS, based on LZ77algoritm

(30% less on the wire when doing compressions)

Active Manager (the brain of Exchange HA)

  • New in 2010
  • Manages *overs
  • Runs on every server in the DAG
  • Selects best available copy on failovers

 Active manager is code that runs in cluster service (not a service)

  • Active manager client runs on CAS and HUB
    • Failover can be performed in 30 seconds or less, that why it it not stored in AD. AD could have 15 min between replication.                
  • PAM holds the default cluster group

Best copy selection

  • Active Manager selects the “best” copy to become the new active copy when the existing active copy fails
  • Behavior difference between RTM and SP1
    • List of potential passive copies is sorted diff when AutoDatabaseMountDial is set to Lossless

 

Improvements in Service pack (replication and copy)

Continues replication changes

  • Block mode (shipping blocks during replications)
    • Enhanced to reduce data loss
    • Eliminates log drive as single point of failure
    • Automatically switched between modes
      • File mode
      • Block mode

Relocate and distribute load Scripts

                             RedistribureAtivedatabases.ps1

DAG Maintenance Scripts

                             StartSAGServerMaintenance.ps1

Exchange Management Console enhancement in SP1

                             Manage DAG IP addresses

                             Manage witness/directory and