Friday, December 31, 2010

Windows Server 2008 R2 Disks

Windows Server 2008 R2 enables administrators to define how disks are presented and used within the system. Depending on the type and size of a disk, administrators can determine which particular type of disk and volumes they should consider deploying on their systems.

Windows disks can be defined as basic or dynamic disks. Furthermore, these same disks can be defined as Master Boot Record (MBR) or GUID Partition Table (GPT) disks. A simple way to clearly differentiate how to choose between these disk types is to consider that basic disks only support simple volumes, whereas dynamic disks allow logical volumes to be created across multiple physical disks. Choosing between MBR and GPT disks depends on the size of the disk, as well as understanding how many partitions you will need to create on the disk.

Windows Server 2008 R2 also supports VHD or virtual hard disks, for Hyper-V virtual machines. VHD disks can now also be created and mounted directly within a Windows host operating system, regardless of whether the Windows Server 2008 R2 system is hosting the Hyper-V role.

Master Boot Record Disks
Master Boot Record (MBR) disks utilize the traditional disk configuration. The configuration of the disk, including partition configuration and disk layout, is stored on the first sector of the disk in the MBR. Traditionally, if the MBR became corrupted or moved to a different part of the disk, the data became inaccessible. MBR disks have a limitation of three primary partitions and a single extended partition that can contain several logical drives. Choosing to create an MBR disk should provide administrators with a more compatible disk that can easily be mounted and/or managed between different operating system platforms and third-party disk management tools.

GUID Partition Table (GPT) Disks
GPT disks were first introduced in Windows with Windows Server 2003 Service Pack 1. GPT disks are recommended for disks that exceed 2TB in size. GPT disks can support an unlimited number of primary partitions and this can be very useful when administrators are leveraging large external disk arrays and need to segment data for security, hosting, or distributed management and access. GPT disks are only recognized by Windows Server 2003 SP1 and later Windows operating systems. Attempting to manage a GPT disk using a previous operating system or third-party MBR disk management tool will be blocked and virtually inaccessible.

Basic Disk
A Windows disk is defined as a basic or a dynamic disk regardless of whether the disk is an MBR or a GPT disk. A basic disk supports only simple volumes or volumes that exist on a single disk and partition within Windows. Basic disks contain no fault tolerance managed by the Windows operating system, but can be fault tolerant if the disk presented to Windows is managed by an external disk controller and is configured in a fault-tolerant array of disks. Basic disks are easier to move across different operating systems and usually are more compatible with Windows and third-party disk and file system services and management tools. Basic disks also support booting to different operating systems stored in separate partitions. Furthermore, and most important, if the disk presented to Windows is from a SAN that includes multiple paths to the disk, using a basic disk will provide the most reliable operation as a different path to the disk might not be recognized if the disk is defined within Windows as a dynamic disk.

Dynamic Disk
Dynamic disks extend Windows disk functionality when managing multiple disks using Windows Server 2008 R2 is required. Windows administrators can configure dynamic disks to host volumes that span multiple partitions and disks within a single system. This allows administrators to build fault-tolerant and better performing volumes when RAID controllers are not available or when a number of smaller disks need to be grouped together to form a larger disk.

In some server deployments, dynamic disks are required as the disk controllers do not support the necessary performance, fault-tolerance, or volume size requirements to meet the recommended system specifications. In these cases, dynamic disks can be used to create larger volumes, fault-tolerant volumes, or volumes that can read and write data across multiple physical disks to achieve higher performance and higher reliability. Dynamic disks are managed by the operating system using the Virtual Disk Service (VDS).

Virtual Hard Disks
Virtual hard disks or VHDs are used by virtual machines to emulate Windows disks.
Virtual hard disks can be created on an existing Windows Server 2008 R2 system using the Hyper-V Management console or they can be created directly using the Disk Management console. VHDs are primarily created on the Windows host system as a file on an existing Windows volume that has a .vhd extension. VHD disks can be created to be fixed size or dynamically expanding. A fixed-sized VHD that is 10GB in size will equate to a 10GB file on the Windows host server volume. A dynamically expanding VHD file will expand as files are stored on it, only as necessary. VHD files can easily be moved across servers and between virtual machines, and also can be expanded quite easily, granted that the VHD is not in use and there is ample free space on the host volume. VHD files can be attached directly to a Windows Server 2008 R2 host using the Disk Management console, unlike in previous releases, which required scripts to mount the file. This added functionality is a needed improvement to the integrated VSS Hyper-V backup functionality, included with Windows Server Backup and available to third-party backup software vendors.

Source of Information : Sams - Windows Server 2008 R2 Unleashed

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