3.4.3 MxDB for SQL Server Installation and Administration Guide

Chapter 3: Configuration and Operation 43

Manage MSDTC: Microsoft Distributed Transaction Coordinator

(MSDTC) is used to coordinate transactions between different SQL

instances running on different nodes in the cluster. There is one MSDTC

service on each machine.

When the “Manage MSDTC” box is checked, MxDB for SQL Server

virtualizes MSDTC, thus enabling transactions that span one or more

Virtual SQL Servers. However, the following limitations exist when using

a Virtual SQL Server with MSDTC.

• Because only one MSDTC resource exists per machine, you can define

MSDTC support for only one Virtual SQL Server per machine. You

can, however, define other Virtual SQL Servers that do not support

MSDTC. The PolyServe Management Console will grey out the

MSDTC switch when a Virtual SQL Server has already been defined

as primary on this node.

• If two MSDTC-enabled Virtual SQL Servers share the same backup

and both Virtual SQL Servers fail, the first server to come up will lock

the MSDTC resource, preventing the other Virtual SQL Server from

starting.

• A failure of MSDTC is considered a failure of the SQL instance.

• You cannot use COM+ components or MSMQ on a node where

MSDTC has been virtualized.

For more information about MSDTC, see the PolyServe Knowledge Base

article “Configure or Rebuild MSDTC on Windows 2003.”

Policy: The policy determines the failback action that the Virtual SQL

Server will take following a failover to a backup node.

•

AUTOFAILBACK. This policy is intended to return the Virtual SQL

Server to its original configuration, or as close to it as possible. After

the Virtual SQL Server fails over to a backup node, the ClusterPulse

process watches the health of the nodes higher in the list of servers for

that Virtual SQL Server. When the health of one of these nodes is equal

to or greater than the backup node where the Virtual SQL Server

currently resides, the Virtual SQL Server will automatically attempt to

fail back to that node.