Logical Disk Manager
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The Logical Disk Manager is an implementation of a logical volume manager for Microsoft Windows NT, developed by Microsoft and Veritas Software. It was introduced with the Windows 2000 operating system, and is supported in Windows XP, Windows Server 2003 and Windows Vista.
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[edit] Overview
Basic storage involves dividing a disk into primary and extended partitions.[1] This is the way that all versions of Windows that were reliant on DOS handled storage took, and disks formatted in this manner are known as basic disks. Dynamic storage involves the use of a single partition that covers the entire disk, and the disk itself is divided into volumes or combined with other disks to form volumes that are greater in size than one disk itself. Volumes can use any supported file system.
Basic disks can be upgraded to dynamic disks, however when this is done the disk cannot easily be downgraded to a basic disk again. To perform a downgrade, data on the dynamic disk must first be backed up onto some other storage device. Second, the dynamic disk must be re-formatted as a basic disk (erasing all data). Finally, data from the backup must be copied back over to the newly re-formatted basic disk.
Dynamic disks provide the capability for software implementations of RAID. The main disadvantage of dynamic disks in Microsoft Windows is that they can only be recognized under certain operating systems, such as Windows 2000 or later (excluding home versions such as Windows XP Home Edition, and Windows Vista Home Basic and Premium[2]), or the Linux kernel starting with version 2.4.8.
Dynamic disks under Windows are provided with the use of databases stored on disk(s). The volumes are referred to as dynamic volumes. It is possible to have 2000 dynamic volumes per dynamic disk, but the maximum recommended by Microsoft is 32.
[edit] Partition table types
| ID (GUID Partition Table and MBR Partition Table) | Description |
|---|---|
GPT: 5808C8AA-7E8F-42E0-85D2-E1E90434CFB3MBR: None1 |
"metadata" partition. The area of the disc that is used for holding configuration data that describe the volumes that LDM manages. |
GPT: AF9B60A0-1431-4F62-BC68-3311714A69ADMBR: 0x42 |
"data" partition. The area of the disc that is used for holding LDM volumes themselves. |
Note 1: On a disk partitioned with the MBR Partition Table scheme, the Logical Disk Manager metadata are not stored in a partition, but are stored in a 1MiB area at the end of the disk that is not assigned to any partition.[3] The disc partitioning tools in Windows XP will not use that area for disk partitions, but the tools in other operating systems might.
[edit] Basic volumes and dynamic volumes
Dynamic volume is Microsoft proprietary format developed together with Veritas (now acquired by Symantec)[4][5]. Basic volumes and dynamic volumes differ in ability to extend storage beyond one physical disk. The basic partitions are confined to one disk and their size is fixed. Dynamic volumes allow to adjust size and to add more free space either from the same disk or another physical disk. Dynamic volumes using space on different physical disks are called spanned volumes. Presently spanned volume can use a maximum of 32 physical disks.
The main differences between basic and dynamic disks are[6][7]:
- Dynamic disks support multipartition volumes; basic disks do not.
- Windows stores basic disk partition information in the registry and dynamic disk partition information on the disk
With basic disks, only up to 4 total (primary + extended) partitions can be created. Dynamic disks allow more flexible configuration without the need to restart the system. Some space at the end of the disk is reserved by Setup in case upgrading the disk to a dynamic disk is required. Dynamic disk information is saved at the end of the disk. The amount that is reserved is a minimum of one cylinder, or 1MB, whichever is greater. One cylinder can be up to 8MB (the reason why there is a remaining 8 MB unused partition every time windows setup is used to create a partition), depending on drive geometry and translation.
The operations common to basic and dynamic disks are the following:
- Check disk properties, such as capacity, available free space, and current status.
- View volume and partition properties, such as size, drive-letter assignment, label, type, and file system.
- Establish drive-letter assignments for disk volumes or partitions, and for CD-ROM devices.
- Establish disk sharing and security arrangements for a volume or partition.
- Upgrade a basic disk to dynamic, or revert a dynamic disk to basic.
[edit] See also
[edit] References
- ^ "How Basic Disks work". Microsoft TechNet. http://technet2.microsoft.com/WindowsServer/en/Library/bdeda920-1f08-4683-9ffb-7b4b50df0b5a1033.mspx.
- ^ "Windows Vista support for large-sector hard disk drives". http://support.microsoft.com/kb/923332/. Retrieved on 2007-10-08.
- ^ "How Dynamic Disks work". Microsoft TechNet. http://technet2.microsoft.com/WindowsServer/en/Library/72c515fa-8acf-4de2-90af-ebca62b27f661033.mspx.
- ^ "BVERITAS Storage Foundation for Windows: The Dynamic Disk Advantage - Comparing Dynamic Disks to Basic Disks". Symantec. http://whitepapers.techrepublic.com.com/abstract.aspx?docid=327310.
- ^ "Veritas Storage Foundation for Windows by Symantec (PDF)". Symantec. http://eval.symantec.com/mktginfo/enterprise/fact_sheets/ent-datasheet_storage_foundation_for_windows_5.0_01-2007.en-us.pdf.
- ^ "Basic and Dynamic Disks". Microsoft MSDN. http://msdn.microsoft.com/en-us/library/aa363785(VS.85).aspx.
- ^ "Dynamic vs. Basic Storage in Windows 2000". Microsoft Support. http://support.microsoft.com/kb/175761/EN-US/.
