Specifications
72 CHAPTER 4 High Availability and Virtualization Enhancements
SQL Server 2008 R2 Virtualization and Hyper-V
Virtualization is one of the hottest topics of discussion in almost every SQL Server architecture
design session or executive brieng session, mainly because organizations are beginning to
understand the immediate and long-term benets virtualization can offer them. SQL Server
virtualization not only promises to be very positive and rewarding from an environmental
perspective—reducing power and thermal costs which translate to green IT—it also promises
to help organizations achieve strategic business objectives and consolidation goals, including
lower hardware costs, smaller data centers, and less management associated with SQL Server.
As a result, increasing numbers of organizations are showing interest in virtualizing their
SQL Server workloads, including their test, staging, and even production environments. This
trend toward virtualization has undoubtedly become stronger with the release of Windows
Server 2008 R2, which includes Live Migration and Cluster Shared Volumes (CSV). By leverag-
ing Live Migration and CSV, organizations can achieve high availability for SQL Server virtual
machines (VMs). In addition, it is possible to move virtualized SQL Server 2008 R2 guest oper-
ating systems between physical Hyper-V hosts without any perceived downtime.
Live Migration Support Through CSV
Live Migration is a new Hyper-V feature in Windows Server 2008 R2 that is used to increase
high availability of SQL Server VMs. By leveraging the new Live Migration feature, organiza-
tions can transparently move SQL Server 2008 R2 VMs from one Hyper-V physical host to
another Hyper-V physical host within the same cluster, without disrupting the services of the
guest operating system or SQL Server application running on the VM. This is achieved via an
intricate process. First, all VM memory pages are transferred from the source Hyper-V physi-
cal host to the destination Hyper-V physical host. Second, any VM modications to the VMs
memory pages on the source Hyper-V physical host are tracked. These tracked and modied
pages are transferred to the physical Hyper-V target computer. Third, the storage handles for
the VMs’ VHD les are moved to the Hyper-V target computer. Finally, the destination VM is
brought online.
The Live Migration feature is supported only when Hyper-V is run on Windows Server
2008 R2. Live Migration can take advantage of the new CSV feature within failover clustering
in Windows Server 2008 R2. The CSVs let multiple nodes in the same failover cluster concur-
rently access the same logical unit number (LUN). Equally important, because a Hyper-V
cluster must be formed as a prerequisite task, Live Migration requires the failover clustering
feature to be added and congured on all of the servers running Hyper-V. In addition, the
Hyper-V cluster hosts require shared storage for the cluster nodes. This can be achieved by
either an iSCSI, Serial Attached SCSI (SAS) or Fibre Channel Storage Area Network (SAN).
Figure 4-5 illustrates a four-node Hyper-V failover cluster with two CSVs and eight SQL
Server guest operating systems. With Live Migration, running SQL Server VMs can be seam-
lessly moved between Hyper-V hosts.