Virtual Disk Services

Virtual Disk Service (VDS) was introduced in Windows Server 2003. It is intended to simplify disk management on NAS, SAN and direct storage, by providing a scriptable command line interface (CLI) for disk management operations. Disks can be defined as JBOD or RAID. Four CLIs are provided

You use DISKPART to manage partitions on both basic and dynamic disks. You also use DISKPART to configure software RAID devices. You can set up a script that will dynamically extend a volume if the used space reaches an alert threshold. The ITZERO site lists out the DISKPART commands and includes some good examples.

You use DISKRAID to configure virtual disks (logical disks that span two or more physical disks) on hardware RAID devices.

You use the DSKMGMT snap-in to remotely manage disks and volumes on other computers running Windows 2000, Windows XP or Windows Server 2003.

You use MOUNTVOL to create, delete or list volume mount points. You can use MOUNTVOL to link volumes without using drive letters.

An especially useful VDS feature is its ability to configure and control disks from several vendors. Most of us populate our SANs with disks from more than one vendor, and each vendor's disks have a different management interface. VDS gives you a single interface to all the disks on your SAN, including NAS systems. The VDS has a command line interface which supports scripts, and that makes the interface even easier, as you can write scripts to perform repetitive work, and VDS then sends the correct commands to the physical disks. For this to work, each hardware provider must translate the VDS standard APIs into instructions specific to their own storage device

VDS Disk Management.

You can use VDS to create partitions on physical or basic disks, to create the volumes that are then mapped to drive letters. These volumes are known as 'simple volumes' and do not span multiple disks. Basic disks are a legacy from pre-Windows 2000 days.
You can also use VDS to create dynamic disks that can consist of either simple volumes or multi-partition volumes that physically span more than a single disk but are logically considered a single volume. You can define dynamic disks as follows, depending on your requirements

• striped (RAID-0), fast performance with no error protection but cheap
• mirrored (RAID-1), fast performance with error protection but expensive
• striped with parity (RAID-5), good performance with error protection and reasonable price

See the RAID section for details. You can use VDS to increase the size of dynamic disks when they are starting to fill up.

You can use VDS to configure, or change the configuration of NAS devices. If you have a NAS 'head' plugged into your SAN, then the storage behind it may be from multiple vendors. You may want to reconfigure that storage as appropriate to your needs. Each storage device will have a different management interface, but if you have VDS, then you can use a common interface for all the different storage boxes.

Multi-path IO

Multi-path Input/Output (MPIO) was introduced in Windows Server 2003

MPIO can provide up to 32 paths to storage, for redundancy on failure, or load balancing to improve performance. MPIO is intended to be used by third party vendors when developing storage products. To do this, they need the driver development kit (DDK), it is not part of the Windows operating system.

Storage Management for SANs

This is a new Microsoft Management Console snap-in facility that you use to centrally manage SAN storage devices. This MMC facility will only work on storage devise that support VDS. You would use it to configure and assign LUNs without having to log into each storage subsystem individually.

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