Notes from the MMMUG August 2009

Wow not many spare chairs, so this was an Exchange 2010 HA session with Ewan Tsang-MacKellar.

Session started with the HA options Exchange 2007 gave us.  Then Ewan introduced us to Exchange 2010 DAG’s (Database Availability Groups).

  • DAG
    • Config information is stored in the AD and the Windows Failover cluster (yeah it’s still used). 
      • It uses the cluster database, heartbeats and the quorum for a failover cluster
    • The DAG is the boundary of replication and failover.
    • Each DAG contains a number of mailbox role servers.  You can have up to 16 servers per DAG and 100 databases.
    • DAGs use Log shipping to move data to other replicas of the database with  1mb Log files. 
      • Replay process similar to Exchange 2010. 
      • Now use TCP sockets NOT SMB for log shipping.
      • Push based log shipping.
      • Can choose the TCP port now too.
      • Supports encryption and compression
    • If a database fails, Exchange will determine the best copy to use.  The CAS will then reconnect outlook automatically.  Failover times are less than 30 seconds (which seem a bit more than Exchange 2007 CCR)
    • Can spread a DAG over Active Directory Sites ;-) Can make it like an SCR target in Exchange 2007.
    • Maximum number of passive copies = # servers in DAG –1 active
    • You can co-locate other roles on a mailbox server that is in a DAG.
    • Database names are unique across an forest
    • Still uses a FSW
    • Incremental Reseeding
    • Continuous Circular logging
  • Active Manager
    • HA’s brain
    • Primary (holds changable state information of each database) and secondary
      • PAM
    • One server in DAG is selected
    • Secondary
      • SAM
      • Helps CAS find the active copy of the database
      • All other servers in DAG
    • On failure of a database will select best copy
      • Copy Status [Good]
      • Catalog (healthy of crawling) [Healthy]
      • Copy Queue length [<10)]
      • Replace queue length
    • If all are okay can you set a preference
  • Backups
    • Uses VSS
    • Can backup active or passive copies or select a server to backup
    • Can use a database copy as a “backup”
      • 7 – 14 day lag copy

Transport HA

  • Shadow Messaging (Redundancy)
    • Hub Transport keeps a copy of a message until it gets confirmation that the message was sent.
    • Uses MsgID to identify each message.  In the event of a failure there is a possibility for duplicate messages to be sent, but the two messages will share a MsgID and “most” email systems will notice this
    • Exchange 2010 keeps a table of MsgID’s for 7 days
    • Size of transport dumpster depends on the time stamp of the worst  log copied.

Other Stuff

  • Autodiscover DNS TTL lower to 5 mins

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