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Datacenter Diskless Boot Technical Preview


Updated: February 29, 2012

Applies To: Windows Server 2012

The Microsoft iSCSI Software Target feature is built into Windows Server 2012, and it lets you create a Storage Area Network (SAN) device on hardware running the Windows operating system. iSCSI Software Target also enables you to network boot multiple computers from a single operating system image that is stored in a centralized location. This improves efficiency, manageability, availability, and security. iSCSI Software Target in Windows Server 2012 can boot hundreds of computers by using a single operating system image and it provides the following benefits:

Cost savings on operating system storage. By using differencing virtual disks, you can use a single operating system image (the “golden image”) to boot up to 256 computers. As an example, in a deployment of Windows Server 2008 R2 HPC edition, the operating system image is approximately 20 GB. A common deployment is to have two mirrored disk drives that act as the boot volume. Rounding the operating system storage to 40 GB per instance, you would need approximately 10 TB of storage — for only the operating system image—to boot 256 computers. With iSCSI Software Target boot, however, you will use 40 GB for the operating system base image, and 2 GB for differencing virtual hard disks (VHDs) per server instance, totaling 552 GB for the operating system images. This provides a savings of over 90% on storage for the operating system images alone.

Controlled operating system images make it more secure and easy to manage. Some enterprises require that data be secured by physically locking storage in a centralized location. In this scenario, servers access the data remotely, including the operating system image. With iSCSI Software Target boot, administrators can centrally manage the operating system boot images, and control which applications to put in the golden image.

Rapid deployment. Because the golden image is a sysprepped operating system image, when the computers boot from the golden image, they skip the file copying and installation phase that occurs during Windows Setup, and they go straight to the customization phase. In our testing, we deployed 256 computers in 34 minutes.

Fast recovery. Because the operating system images are hosted on the iSCSI Software Target server, if the diskless client needs to be replaced, the new computer can point to the operating system image, and boot up immediately.

A SAN boot is a solution that has been offered from various vendors. In Windows Server 2012, the new iSCSI Software Target feature provides this network boot capability on commodity hardware.

iSCSI Software Target can be installed as part of the File Server role.

The easy management experience is provided through Server Manager. For automation, you can use the corresponding Windows PowerShell cmdlets.

This feature does not require special hardware for functional verification. In data centers with large-scale deployments, the design should be validated against specific hardware. For reference, Microsoft internal testing indicated that for a 256-iSCSI boot deployment, 24x15k-RPM (revolution per minute) disks in a RAID 10 configuration were required for storage. A network bandwidth of 10 GB is optimal. A general estimate is 60 iSCSI boot servers per 1 GB network adapter. However, an iSCSI boot-capable network adapter is not required for this scenario. If the network adapter does not support it, a software boot loader can be used (such as iPXE open source boot firmware).

The iSCSI Software Target feature in Windows Server 2012 supports diskless network boot without the need for special hardware or additional software. iSCSI Software Target fully complies with the iSCSI protocol as specified by the Internet Engineering Task Force. A key component to this feature is that it supports differencing of virtual hard disks. This is critical in the boot scenario because multiple servers running Windows Server 2012 can boot by using only one base image.

iSCSI Software Target accomplishes diskless boot as follows:

  • iSCSI Software Target supports creating differencing virtual disks based on a golden image.

  • Each diskless client boots from its own differencing virtual disk.

  • The diskless client reads from the golden image, and writes to its own differencing VHD.

Because the image is hosted in a centralized place, storage space savings are realized on operating system deployment. That can translate into freed-up storage space that was previously allocated to operating system boot images or budget savings because you no longer need to purchase hard disks for this purpose and the power to cool them.

In Windows Server 2012, the scale of iSCSI boot has increased to 256. Therefore, the clustered target can support 256 boot clients, and it does not experience operating system errors with iSCSI Software Target service failover from one clustered node to another.

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