Virtual Disks and Snapshots

Published: July 10, 2009

Applies To: Microsoft iSCSI Software Target

The disks you create by using iSCSI Software Target are iSCSI virtual disks, which are files in the fixed virtual hard disk (VHD) format. These virtual disks offer flexible and effective storage. They can be extended to provide extra capacity on demand, enable efficient storage utilization, minimize the time that is required to create disks, and minimize the down time that is typically required to install new disks.

Snapshots

To facilitate backup and recovery operations, you can schedule and create snapshots of iSCSI virtual disks. A snapshot is a point-in-time, read-only copy of an iSCSI virtual disk. Snapshots are useful for backups and for data mining. Snapshots offer the following advantages:

  • Snapshots can be scheduled to be created automatically.

  • Snapshots are space-efficient because they are differential copies.

  • Snapshots are useful for fast system recovery of files and volumes, in case of accidental data deletion by a user, overwritten data, or data corruption resulting from a malicious program.

  • Snapshots can be mounted locally or exported to facilitate backup and recovery operations.

  • Snapshots do not require that you close files or stop programs when you create them, so application servers can continue servicing clients without disruption.

noteNote
Snapshots that are created on the iSCSI target server are crash consistent. Most modern file systems can recover from this state. To create an application-consistent snapshot, the snapshot must be created from the iSCSI initiator computer by using the Microsoft iSCSI Software Target Volume Shadow Copy Service Hardware Provider and third-party backup software that works with Volume Shadow Copy Service.

Hardware Providers

To support management of iSCSI virtual disks and snapshots, you can install the appropriate hardware providers. These hardware providers, which are available on the installation CD, include:

  • Microsoft iSCSI Software Target Virtual Disk Service Hardware Provider.

    Virtual Disk Service (VDS) is a set of application programming interfaces (APIs) that provides a single interface for managing disks. VDS provides an end-to-end solution for managing storage hardware and disks, and for creating volumes on those disks. The Microsoft iSCSI Software Target VDS Hardware Provider is required to manage virtual disks on a storage subsystem.

    You install the Microsoft iSCSI Software Target VDS Hardware Provider on each iSCSI initiator computer running a storage management application (such as Storage Manager for SANs) that uses the hardware provider to manage storage, as described later in this guide.

  • Microsoft iSCSI Software Target Volume Shadow Copy Service Hardware Provider.

    iSCSI snapshots are created using Volume Shadow Copy Service (VSS) and a storage array with a hardware provider that works with VSS. A Microsoft iSCSI Software Target VSS Hardware Provider is required to create transportable snapshots of iSCSI virtual disks and to create application consistent snapshots from iSCSI initiators.

    You install this hardware provider on the iSCSI initiator server and the server that is to perform backups.

Command Line Utilities for Hardware Providers

You can perform many of the administrative tasks for the Microsoft iSCSI Software Target from the command prompt by using standard Windows Server 2008 utilities. This topic lists some of the commands that you might find useful. See the command help in Help and Support for more information.

VDS Hardware Provider Related Command Line Tools

The following commands can be used to work with disks and volumes from the command prompt:

  • MountVol.exe – MountVol is used to create, delete, or display volume mount points.

  • DiskRaid.exe – DiskRaid is used to create, delete, and optimize physical and logical raid arrays.

VSS Hardware Provider Related Command Line Tools

The following tools can be used to work with VSS from the command prompt:

  • VSSAdmin.exe – VSSAdmin is used to manage the Volume Shadow Copy Service, including creating, resizing, and deleting VSS allocations on volumes.

  • DiskShadow.exe – DiskShadow is a tool for working with VSS, similar to VSSAdmin, but also lets you work with snapshots.

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