Logical Disk Manager
Encyclopedia
The Logical Disk Manager (diskmgmt.msc) 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
, Windows Vista
and Windows 7. The MMC
-based Disk Management snap-in hosts the Logical Disk Manager.
-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 versions such as Windows XP
Home Edition, and Windows Vista
Home Basic and Premium), 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.
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. The disc partitioning tools in Windows XP
will not use that area for disk partitions, but the tools in other operating systems might.
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:
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:
alignment boundary, ignoring the previous conventions called "drive geometry" or "CHS"
. In other words, Vista's Disk Management acts like it is using a non-standard CHS geometry of 2048 sector
s per track
/head
and 1 track/head per cylinder (the sectors being of 512 bytes so that 2048 sectors is 1 MiB
).
or FAT
http://www.multibooters.co.uk/quirks.html (see section "You may see several primary partitions on a drive").
Logical volume management
In computer storage, logical volume management or LVM provides a method of allocating space on mass-storage devices that is more flexible than conventional partitioning schemes...
for Microsoft Windows NT, developed by Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
and Veritas Software
VERITAS Software
Veritas Software Corp. was an international software company that was founded in 1983 as Tolerant Systems, renamed Veritas Software Corp. in 1989, and merged with Symantec in 2005. It was headquartered in Mountain View, California...
. It was introduced with the Windows 2000
Windows 2000
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
operating system, and is supported in Windows XP
Windows XP
Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
, Windows Server 2003
Windows Server 2003
Windows Server 2003 is a server operating system produced by Microsoft, introduced on 24 April 2003. An updated version, Windows Server 2003 R2, was released to manufacturing on 6 December 2005...
, Windows Vista
Windows Vista
Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
and Windows 7. The MMC
Microsoft Management Console
Microsoft Management Console is a component of Windows 2000 and its successors that provides system administrators and advanced users an interface for configuring and monitoring the system.- Snap-ins and consoles :...
-based Disk Management snap-in hosts the Logical Disk Manager.
Overview
Basic storage involves dividing a disk into primary and extended partitions. This is the route that all versions of Windows that were reliant on DOSDOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
-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
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
.
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
Windows 2000
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
or later (excluding versions such as Windows XP
Windows XP
Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
Home Edition, and Windows Vista
Windows Vista
Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
Home Basic and Premium), or the Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
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.
Partition table types
| ID (GUID Partition Table GUID Partition Table In computer hardware, GUID Partition Table is a standard for the layout of the partition table on a physical hard disk. Although it forms a part of the Extensible Firmware Interface standard , it is also used on some BIOS systems because of the limitations of MBR partition tables, which restrict... and MBR Partition Table Master boot record A master boot record is a type of boot sector popularized by the IBM Personal Computer. It consists of a sequence of 512 bytes located at the first sector of a data storage device such as a hard disk... ) | Description |
|---|---|
GPT: 5808C8AA-7E8F-42E0-85D2-E1E90434CFB3MBR: None |
"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. |
On a disk partitioned with the MBR Partition Table scheme, the Logical Disk Manager metadata
Metadata
The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
are not stored in a partition, but are stored in a 1MiB
Mebibyte
The mebibyte is a multiple of the unit byte for digital information. The binary prefix mebi means 220, therefore 1 mebibyte is . The unit symbol for the mebibyte is MiB. The unit was established by the International Electrotechnical Commission in 2000 and has been accepted for use by all major...
area at the end of the disk that is not assigned to any partition. The disc partitioning tools in Windows XP
Windows XP
Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
will not use that area for disk partitions, but the tools in other operating systems might.
Basic volumes and dynamic volumes
Dynamic volume is a Microsoft proprietary format developed together with Veritas (now acquired by Symantec).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:
- 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
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.
Compatibility problems
Disk Management in Windows Vista creates partitions according to a 1-MiBMIB
MIB may refer to any of several concepts:* Master of International Business, a postgraduate business degree* Melayu Islam Beraja, the adopted national philosophy of Brunei* Motion induced blindness, a visual illusion in peripheral vision...
alignment boundary, ignoring the previous conventions called "drive geometry" or "CHS"
Cylinder-head-sector
Cylinder-head-sector, also known as CHS, was an early method for giving addresses to each physical block of data on a hard disk drive. In the case of floppy drives, for which the same exact diskette medium can be truly low-level formatted to different capacities, this is still true.Though CHS...
. In other words, Vista's Disk Management acts like it is using a non-standard CHS geometry of 2048 sector
Sector
- Places :* Sector, Devon, a location in the county of Devon in south-western England* Sector, West Virginia, an unincorporated community in Hampshire County, West Virginia, United States of America- In computing :...
s per track
Track (disk drive)
A disk drive track is a circular path on the surface of a disk or diskette on which information is magnetically recorded and from which recorded information is read....
/head
Disk read-and-write head
Disk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...
and 1 track/head per cylinder (the sectors being of 512 bytes so that 2048 sectors is 1 MiB
MIB
MIB may refer to any of several concepts:* Master of International Business, a postgraduate business degree* Melayu Islam Beraja, the adopted national philosophy of Brunei* Motion induced blindness, a visual illusion in peripheral vision...
).
Compatibility problems with using a 1-MiB alignment boundary
- Extended partition tables that are edited with Vista Disk Management should not be edited with Windows XP Disk Management. XP Disk Management may delete these extended partitions without warning. One way to correct these mixed partition tables is to delete all partitions (reboot or reconnect drive) and use only one partition editor on the drive.
- You may not be able to install XP or Windows Server 2003 to partitions created with Vista Disk Management.
- These 1 MiB alignments ignore prior CHSCylinder-head-sectorCylinder-head-sector, also known as CHS, was an early method for giving addresses to each physical block of data on a hard disk drive. In the case of floppy drives, for which the same exact diskette medium can be truly low-level formatted to different capacities, this is still true.Though CHS...
conventions such as the regular intervals at which partitions begin and end, and the distance between the extended boot records and their logical drives.
- Other operating systems (perhaps DOSDOSDOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
programs used by backup or recovery software), boot loaders, or partitioners may have problems viewing or editing partitions that do not follow a CHS alignment. (Generally, unpredictable results may come from using more than one partitioner on the same partition tablePartition tableThe term partition table is most commonly associated with partition table but it may be used generically to refer to other "formats" that divide a disk drive into partitions, such as: GUID Partition Table, Apple partition map, or BSD disklabel.An alternative term to generically refer to partition...
without checking the alignments with tools such as Ranish Partition ManagerRanish Partition ManagerRanish Partition Manager is a freeware hard disk partition editor, disk cloning tool, and boot manager, that gives a high level of control for creating multi-boot systems. It is available on the freeware live cd SystemRescueCD and the Ultimate Boot CD...
. For example, operating systemOperating systemAn operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
installers usually start with a partition editorPartition editorA partition editor is a kind of utility software designed to view, create, alter and delete disk partitions on a computer storage device, most commonly a hard disk, but often a USB flash drive or other storage medium.A partition is a section or segment of the storage space on a storage device...
so it may be important that this uses the same alignments as the previous partition editors, if all partitions are not deleted (and the computer reset) before installing the operating system. The variation in CHS geometry is almost always a different number of heads per cylinder, for example, 240 instead of 255. However, partition editors may seem to ignore this sort of geometry in some situations. "Head" and "track" mean the same thing in this context.)
Advantages of using a 1-MiB alignment boundary
- Microsoft states that on large-sector drives, also known as advanced formatAdvanced FormatAdvanced Format is a generic term pertaining to any sector format used to store data on the magnetic disks in hard disk drives that exceeds 512 to 520 bytes per sector. Advanced Format is also considered a milestone technology in the history of hard-drive storage, where data has been processed in...
, there is a "performance issue" when the starting offset of the first partition, is an "odd" number. This partition alignment offset also affects newer generation drives not necessarily specified as advanced formatAdvanced FormatAdvanced Format is a generic term pertaining to any sector format used to store data on the magnetic disks in hard disk drives that exceeds 512 to 520 bytes per sector. Advanced Format is also considered a milestone technology in the history of hard-drive storage, where data has been processed in...
such as SSDSSD-Computing:* Solid-state drive, a type of data storage device which uses memory rather than rotating media* Seven-segment display, a display which uses 7 segments to display mostly numbers* System sequence diagram, a type of UML software engineering diagram...
drives. Misalignment causes severe degradation not only with random write performance, but also with sequential write performance (normally to a far lesser degree).: "In earlier versions of Windows, the default starting offset for the first partition on a hard disk drive was sector 0x3F. Because this starting offset was an odd number, it could cause performance issues on large-sector drives because of misalignment between the partition and the physical sectors. In Windows Vista, the default starting offset will generally be sector 0x800."
-
- The "starting offset" refers to the sectors before the partition. "3F" is a hexadecimal value; in decimal that is "63". This is the size of one head (or "track") in terms of a standard CHS geometryCylinder-head-sectorCylinder-head-sector, also known as CHS, was an early method for giving addresses to each physical block of data on a hard disk drive. In the case of floppy drives, for which the same exact diskette medium can be truly low-level formatted to different capacities, this is still true.Though CHS...
. The hex value "800", in decimal form is 2048, so this is referring to the first MiBMIBMIB may refer to any of several concepts:* Master of International Business, a postgraduate business degree* Melayu Islam Beraja, the adopted national philosophy of Brunei* Motion induced blindness, a visual illusion in peripheral vision...
of space, from the start of the disk. Because a 1-MiB alignment boundary is used by the Vista partitioner(s), 1 MiB is "reserved for" the MBRMBRMBR may refer to:* Minerações Brasileiras Reunidas, a division of Caemi* Malaysian Book of Records* Master boot record, the first sector of a partitioned data storage device, used for booting* Membrane bioreactor* Memory buffer register...
, instead of the traditional 63 sectors (31.5 KiB). Note that the MBRMBRMBR may refer to:* Minerações Brasileiras Reunidas, a division of Caemi* Malaysian Book of Records* Master boot record, the first sector of a partitioned data storage device, used for booting* Membrane bioreactor* Memory buffer register...
is only one sector in size, but many softwares use these 63 sectors of "free space" (or any "free space" preceding the partition) for their purposes. 63 sectors is the minimum space that should be reserved for the MBR or an Extended Boot Record(EBREBREBR may refer to:* Experimental Breeder Reactor I, a nuclear research reactor* Experimental Breeder Reactor II, another nuclear research reactor* Mk 14 Mod 0 Enhanced Battle Rifle, an M14 battle rifle variant...
).
- The "starting offset" refers to the sectors before the partition. "3F" is a hexadecimal value; in decimal that is "63". This is the size of one head (or "track") in terms of a standard CHS geometry
-
- What this means is that, if there were no partitions on a disk when it was booted, a partition was created using standard CHS geometry (as would be used by most partition editors such as MS DOS fdisk, Linux fdisk, Ranish Partition Manager, or an XP installation disk), and this partition was created at the start of the disk, then the partition will start on the 2nd head. The partition could not begin at the first sector because the MBRMBRMBR may refer to:* Minerações Brasileiras Reunidas, a division of Caemi* Malaysian Book of Records* Master boot record, the first sector of a partitioned data storage device, used for booting* Membrane bioreactor* Memory buffer register...
located there, so instead it starts the partition on the second head. When primary partitions are created anywhere else (following typical CHS geometry alignment) they start at the beginning of a cylinder.
- What this means is that, if there were no partitions on a disk when it was booted, a partition was created using standard CHS geometry (as would be used by most partition editors such as MS DOS fdisk, Linux fdisk, Ranish Partition Manager, or an XP installation disk), and this partition was created at the start of the disk, then the partition will start on the 2nd head. The partition could not begin at the first sector because the MBR
-
- If a computer is booted with no partitions defined, and the first partition is created with the Vista installation disk, it will instead use the 1-MiB alignment. (The partitioner on the Vista installation disk follows the 1-MiB alignment just as Vista Disk Management does.) By following a 1-MiB alignment, all partitions will have an even numbered offset (so long as no other partitioner is used on the drive).
- Using a 1-MiBMIBMIB may refer to any of several concepts:* Master of International Business, a postgraduate business degree* Melayu Islam Beraja, the adopted national philosophy of Brunei* Motion induced blindness, a visual illusion in peripheral vision...
alignment boundary allows safer editing of the partition table with Vista Disk Management.
- Partition tables using a CHS geometry (or some mix of alignments) may prevent Vista from resizing partitions or it may produce unconventional partition tables. For example, the endings of the "EBR extended partitions" (type 05) may overlap other partitions, and it will leave unprecedented amounts of space between an extended boot record and its logical drive. Ranish Partition ManagerRanish Partition ManagerRanish Partition Manager is a freeware hard disk partition editor, disk cloning tool, and boot manager, that gives a high level of control for creating multi-boot systems. It is available on the freeware live cd SystemRescueCD and the Ultimate Boot CD...
does not show an error if there are more than 63 sectors between the EBR and its logical volume, so long as the EBRs and VBRVolume Boot RecordA volume boot record is a type of boot sector introduced by the IBM Personal Computer...
s are on the first sector of any track (head). If either the VBR or the EBR are not on the first sector of a head, Ranish Partition ManagerRanish Partition ManagerRanish Partition Manager is a freeware hard disk partition editor, disk cloning tool, and boot manager, that gives a high level of control for creating multi-boot systems. It is available on the freeware live cd SystemRescueCD and the Ultimate Boot CD...
shows the "partition" in red and when the partition is highlighted, this error message appears: "Boot sector doesn't have valid information". Using the 1-MiB alignment boundary will not put VBRs or EBRs on the first sector of a track (according to any standard CHS geometry) and Vista Disk Management will not use the CHS geometry of a partition table created with a different partition editor.
- A disk that is solely partitioned with Vista Disk Management can create partitions in exact MiB sizes and never leave leftover bits of space between partitions.
- With Vista DM, all the logical drives besides the one nearest the beginning of the extended partition (type 0F), usually reserve exactly one additional MiB, for an extended boot record, instead of the 63 sectors (31.5 KiB) that is most commonly reserved according to alignments based on a CHS geometry. If other partition editors are used on the disk then Vista DM may reserve different amounts of space for the EBRs.
Threatening Usage
General recommendation to work on drives and partitions only after prior backing up should be strongly obeyed.Delete partition
The function delete partition works without any prior confirmation on impact for other partitions and may destroy other partitions without prior notice. This function is recommended to be ignored as far as no backup is available. Other vendors' solutions provide protection for other partitions.Incorrectly displaying partition tables
Vista and Windows 7 Disk Management may incorrectly display logical drives as primary partitions, particularly when they are not labeled (or formatted?) as NTFSNTFS
NTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, Windows Vista, and Windows 7....
or FAT
File Allocation Table
File Allocation Table is a computer file system architecture now widely used on many computer systems and most memory cards, such as those used with digital cameras. FAT file systems are commonly found on floppy disks, flash memory cards, digital cameras, and many other portable devices because of...
http://www.multibooters.co.uk/quirks.html (see section "You may see several primary partitions on a drive").
See also
- Logical volume managementLogical volume managementIn computer storage, logical volume management or LVM provides a method of allocating space on mass-storage devices that is more flexible than conventional partitioning schemes...
- Logical Volume ManagerLogical Volume ManagerLogical Volume Manager may refer to:*Logical Volume Manager *Logical Volume Manager...
- List of Microsoft Windows components
- diskpartDiskpartIn computing, diskpart is a command-line hard disk partitioning utility included in versions of the Windows NT operating system line from Windows 2000 onwards, replacing fdisk which was used in MS-DOS based operating systems....