Learn Exchange 2013 with me! - High Availability and Site Resilience

  • Article

Exchange 2013 builds on the existing High Availability and Site Resilience features from Exchange 2010. A huge amount of work has been done in many areas to provide better availability and failure isolation.

The use of DAGs and database copies along-with features like Single Item Restore, lagged copies, retention policies continue to provide HA and SR. The high availability platform, the Exchange Information Store and the Extensible Storage Engine (ESE), have all been enhanced to provide greater availability, easier management, and to reduce costs. These enhancements include:

  • Reduction in IOPS over Exchange 2010 – Passive copies in Exchange 2010 DAGs have a very low checkpoint depth (5 MB) which was required for fast failover; this also means that we are aggressively pre-reading the data to be able to keep up with the low checkpoint depth. With Exchange 2013, the checkpoint depth is now 100 MB!! This was possible with some major improvements in ESE/JET. With this higher depth, passive copies are no longer required to be as aggressive with pre-reading the data and this results in a passive copy requiring about 50% of the IOPS compared to an active copy of the mailbox database
  • Managed Availability –Think of this as some “monitoring” (word used loosely :)) for the user experience and not just for the server uptime. I plan to post more on this at a later time as well. In theory, this is a check by the application, against the application to ensure that the service that is provided (eg. OWA) is available to the user and take corrective actions like App Pool recycles Service restarts and in some cases DB failovers to main service to the user.
  • Managed Store - The Managed Store is the name of the newly rewritten Information Store processes in Exchange 2013. The new Managed Store is written in C# and tightly integrated with the Microsoft Exchange Replication service (MSExchangeRepl.exe) to provide higher availability through improved resiliency.
  • Support for multiple databases per disk – We know that 8 TB drives will soon be a reality! We will now be able to have multiple DBs on the same disk, including a combination of active and passive DBs on the same disk
  • AutoReseed – Have a hot spare? Let’s put it to use while you sleep peacefully. Consider a failed disk with an active DB on a server; if we have a hot spare we will put it to use and automatically reseed the DBs on the new disk.
  • Automatic recovery from storage failures – This feature continues the innovation introduced in Exchange 2010 to allow the system to recover from failures that affect resiliency or redundancy. In addition to the Exchange 2010 bugcheck behaviors, Exchange 2013 includes additional recovery behaviors for long IO times, excessive memory consumption by MSExchangeRepl.exe, and severe cases where the system is in such a bad state, threads cannot be scheduled.
  • Lagged copy enhancements – Lagged copies can now care for themselves to a certain extent using automatic log play down. Lagged copies will automatically play down log files in a variety of situations, such as page patching and low disk space scenarios. If the system detects that page patching is required for a lagged copy, the logs will be automatically replayed into the lagged copy to perform page patching. Lagged copies will also invoke this auto replay feature when a low disk space threshold has been reached, and when the lagged copy has been detected as the only available copy for a specific period of time. In addition, lagged copies can leverage Safety Net, making recovery or activation much easier.
  • Single Copy Alert enhancements – The single copy alert introduced in Exchange 2010 is no longer a separate scheduled script. It has been integrated into the managed availability components within the system and is now a native function within Exchange.
  • DAG network auto-configuration – DAGs networks can be automatically configured by the system based on configuration settings. In addition to manual configuration options, DAGs can also distinguish between MAPI and Replication networks and configure DAG networks automatically.

There are a few more that you can read about on https://technet.microsoft.com/en-us/library/dd638137.aspx