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Pieces of the puzzle - Hyper-V hosts, switching, and a SAN
At a very high level, Hyper-V clustering is fairly straightforward. You have two host servers that form a Hyper-V cluster. Host servers store and access virtual machine files located on a SAN. Connection to the SAN is done using iSCSI protocol to make drives on the SAN appear as local drives to Windows Server. Because the virtual machines (VMs) are clustered, they can be moved between servers and provide high availability.
The storage area network, or SAN, is a centralized location for storage of virtual machine files. The SAN is needed because Hyper-V hosts require a place to store virtual machine files that can be shared between multiple hosts. In the event of a host server failure, another Hyper-V host, utilizing cluster technology, can resume operation of virtual machines by assuming control of the virtual drive where the virtual machine’s files are stored. The SAN has to be setup and fully functional before creation of clustered virtual machines.
There are seemingly endless options when it comes to SAN solutions. The solution you choose will likely be dictated more by budget constraints than by system requirements. To illustrate, here are a couple scenarios:
Scenario 1: Software SAN for Small to Medium business with a small budget
A small business might host their SAN on a single server and share some network hardware with the rest of the network. The SAN server might run Windows Server 2008 R2 with a free iSCSI target solution like Microsofti SCS ISoftware Target or Starwind iSCSI SAN. Linux based Openfiler is another option.
Loss of this single server could cause the Hyper-V virtual machines to stop responding. (NOTE: Some vendors, like Starwind Software for example, may have the option of providing highly available storage though by having more than one SAN server).
Scenario 2: Hardware SAN for Large business with a large budget
A large business might host their SAN on server hardware from a vendor such as EMC or NetApp who specializes in building SAN hardware. The solution might also provide virtual drive replication and high availability. Loss of a single server would not prevent Hyper-V virtual machines from functioning normally.
Starwind Software management console
iSCSI Initiators and targets
Regardless of vendor and complexity, the SAN needs to provide iSCSI targets. An iSCSI initiator on the Windows Server 2008 host is used to connect to an iSCSI target on the SAN. Once the connection is established, specific virtual drives are added. In iSCSI, virtual drives are identified by logical unit number (LUN). Each connected LUN is seen by the Windows Hyper-V host as a local drive. The drive can then be formatted for storage of virtual machine configuration and hard drive files.
iSCSI Initiator in Windows Server 2008 R2
In the next posts I’ll be covering switching and additional host requirements for a Hyper-V cluster.