iSCSI High-Availability Block Storage Technical Preview
Updated: February 29, 2012
Applies To: Windows Server 2012
In a virtualized environment, building a host cluster with Windows Server 2012 can limit downtime due to hardware failures. However, this scenario does not help if you need to take down the virtual machine for maintenance. If downtime of any kind is not an option, you should consider creating a virtual machine guest cluster on top of your host cluster—a feature that has become more relevant in Windows Server 2012. This enables you to service the workload by taking one virtual machine node down for maintenance while the others are still running.
In a host cluster only scenario, the cluster service runs inside the parent partition of the Hyper-V-enabled physical computer. The cluster manages the virtual machines, which reduces downtime when you need to make hardware changes or software updates to the parent partition. The cluster also provides the ability to migrate virtual machines to other servers to load balance.
Guest clustering runs inside a Hyper-V guest computer, and it supports high availability for workloads within the virtual machine. If you add guest clustering to the previous scenario, you can manage cluster-aware applications and services by moving applications between virtual machines within the cluster, without downtime. You can use this process for operating system, service, or application updates. In addition, shared block storage is directly presented to the virtual machine by using the Microsoft iSCSI Software Initiator.
Enabling Microsoft iSCSI Software Target to provide block storage leverages your existing Ethernet network. No additional hardware is needed. If high availability is an important criteria, consider setting up a high availability server. With a high availability server, you will need shared storage for the cluster—either hardware Fibre Channel storage or a serial attached SCSI (SAS) storage array.
If you enable guest clustering, you need to provide block storage. Any servers running Windows Server software with Microsoft iSCSI Software Target can provide block storage.
Microsoft iSCSI Software Target is a feature under the File Server role in Windows Server 2012, and it is in full compliance with the iSCSI protocol that is outlined by the Internet Engineering Task Force. The Microsoft iSCSI Initiator provides a way to enable an iSCSI initiator in virtual machines so that they can connect to target servers.
Because iSCSI is an industrial standard, Microsoft iSCSI Software Target interoperates with non-Microsoft implementations of an iSCSI initiator. In a heterogeneous environment with other operating systems, Microsoft iSCSI Software Target can also provide storage access, giving you more choices to access storage.
Windows Server 2012 includes a change in Microsoft iSCSI Software Target when it is used in a clustering configuration. This change improves scalability so that more initiators can connect to the target servers. This supports the goal to provide continuous availability and support workloads with less than 60 seconds of brown time.