First published on TechNet on Oct 22, 2012
As mentioned in my prior post about Storage Spaces, Windows Server 2012 contains many new capabilities. The integrated iSCSI Target happens to be one of those. Many have used the downloadable iSCSI Target for Windows Server 2008 R2 from Microsoft since it was released for internet download. Prior to release for download the Microsoft iSCSI Target was available as a component of Windows Storage Server. Windows Server 2012 contains a native iSCSI Target and there’s no need to download one if you need to make storage available via iSCSI for other systems or virtual machines. No special licenses required. It is worthy to note that the included target is not identical to the downloadable target for Windows Server 2008 R2 – though they both provide block based storage.
The new target contains improvements above and beyond the previous version. For instance, the new iSCSI Target would be of interest to you if you have any new 4k sector drives as it contains support for these newer devices. Development included some enhancements that improve performance rather comprehensively. Additionally, iSCSI virtual disks do not have to be hosted on dedicated physical disks. You may use Windows Server 2012 Storage Spaces to host them. However, incorporation of iSCSI LUNs into a Storage Spaces pool is not supported.
There are a few different ways to manage iSCSI Targets under Windows Server 2012 which may be different than what some administrators may be familiar with previously. Those that have become adept with PowerShell will be happy to know there is yet more PowerShell support for iSCSI Targets. Increased PowerShell support is of no surprise since management interfaces are consistently backed by PowerShell cmdlets. Beyond PowerShell, the MMC snap-in method for managing iSCSI Targets is no longer the way to manage them. You may manage iSCSI Targets via the management interface integrated into Server Manager. As a side note, the iSCSI Initiator remains a separate component with a management interface accessible from the Control Panel.
New in Windows Server 2012 is the Windows Storage Management API (SMAPI) that provides cmdlets for PowerShell and a new set of WMI classes for management of Windows storage. Having these additional interfaces opens up scripting possibilities as well as remote administration through a variety of methods for managing Windows storage. Also new to Windows Server 2012 is the Storage Management Provider (SMP) framework which also works with 3rd party storage. The iSCSI Target included with Windows Server 2012 as released does not include a Storage Management Initiative – Specification (SMI-S) Provider. Therefore, other existing interfaces need to be used for management of targets. The following link suggests that with the introduction of SMAPI that the Virtual Disk Service (VDS) is being deprecated. Perhaps a SMI-S Provider for iSCSI Target is a thing of the future.
If you’ve used one of Microsoft’s iSCSI Targets before, you know that when you create virtual disks for a given target, the underlying storage resides in a VHD file. In Windows Server 2012, these iSCSI Target VHD files are completely compatible with Hyper-V (and vice versa) for VHDs up to 2TB. Therefore, if you create a VHD using iSCSI Target that is within the constraints of Hyper-V, you can port that VHD directly over for use with a Hyper-V virtual machine. However, Hyper-V under Windows Server 2012 introduces a new virtual hard disk format known as VHDx. This format is not supported by the iSCSI Target.
Prior releases of iSCSI Target would allow snapshots to be taken of one of the virtual disks with the ability to revert to a snapshot later. However, the methods used could require lengthy operations to complete the copy. Though the copy operation for snapshots could be slow, applying the snapshot to revert was fairly quick. Windows Server 2012’s implementation of snapshots for iSCSI is based on VSS, much more robust, and uses common VSS features. In addition to VSS support, in Windows Server 2012 the iSCSI Target integrates with Failover Clustering. Therefore, you may create highly available iSCSI targets.
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