[mirror_ubuntu-bionic-kernel.git] / Documentation / ldm.txt


            LDM - Logical Disk Manager (Dynamic Disks)
            ------------------------------------------

Overview
--------

Windows 2000 and XP use a new partitioning scheme.  It is a complete
replacement for the MSDOS style partitions.  It stores its information in a
1MiB journalled database at the end of the physical disk.  The size of
partitions is limited only by disk space.  The maximum number of partitions is
nearly 2000.

Any partitions created under the LDM are called "Dynamic Disks".  There are no
longer any primary or extended partitions.  Normal MSDOS style partitions are
now known as Basic Disks.

If you wish to use Spanned, Striped, Mirrored or RAID 5 Volumes, you must use
Dynamic Disks.  The journalling allows Windows to make changes to these
partitions and filesystems without the need to reboot.

Once the LDM driver has divided up the disk, you can use the MD driver to
assemble any multi-partition volumes, e.g.  Stripes, RAID5.

To prevent legacy applications from repartitioning the disk, the LDM creates a
dummy MSDOS partition containing one disk-sized partition.


Example
-------

Below we have a 50MiB disk, divided into seven partitions.
N.B.  The missing 1MiB at the end of the disk is where the LDM database is
      stored.

  Device | Offset Bytes  Sectors  MiB | Size   Bytes  Sectors  MiB
  -------+----------------------------+---------------------------
  hda    |            0        0    0 |     52428800   102400   50
  hda1   |     51380224   100352   49 |      1048576     2048    1
  hda2   |        16384       32    0 |      6979584    13632    6
  hda3   |      6995968    13664    6 |     10485760    20480   10
  hda4   |     17481728    34144   16 |      4194304     8192    4
  hda5   |     21676032    42336   20 |      5242880    10240    5
  hda6   |     26918912    52576   25 |     10485760    20480   10
  hda7   |     37404672    73056   35 |     13959168    27264   13

The LDM Database may not store the partitions in the order that they appear on
disk, but the driver will sort them.

When Linux boots, you will see something like:

  hda: 102400 sectors w/32KiB Cache, CHS=50/64/32
  hda: [LDM] hda1 hda2 hda3 hda4 hda5 hda6 hda7


Compiling LDM Support
---------------------

To enable LDM, choose the following two options: 

  "Advanced partition selection" CONFIG_PARTITION_ADVANCED
  "Windows Logical Disk Manager (Dynamic Disk) support" CONFIG_LDM_PARTITION

If you believe the driver isn't working as it should, you can enable the extra
debugging code.  This will produce a LOT of output.  The option is:

  "Windows LDM extra logging" CONFIG_LDM_DEBUG

N.B. The partition code cannot be compiled as a module.

As with all the partition code, if the driver doesn't see signs of its type of
partition, it will pass control to another driver, so there is no harm in
enabling it.

If you have Dynamic Disks but don't enable the driver, then all you will see
is a dummy MSDOS partition filling the whole disk.  You won't be able to mount
any of the volumes on the disk.


Booting
-------

If you enable LDM support, then lilo is capable of booting from any of the
discovered partitions.  However, grub does not understand the LDM partitioning
and cannot boot from a Dynamic Disk.


More Documentation
------------------

There is an Overview of the LDM online together with complete Technical
Documentation.  It can also be downloaded in html.

  http://linux-ntfs.sourceforge.net/ldm/index.html
  http://linux-ntfs.sourceforge.net/downloads.html

If you have any LDM questions that aren't answered on the website, email me.

Cheers,
    FlatCap - Richard Russon
    ldm@flatcap.org
Commit	Line	Data
1da177e4 LT	1
	2	LDM - Logical Disk Manager (Dynamic Disks)
	3	------------------------------------------
	4
	5	Overview
	6	--------
	7
	8	Windows 2000 and XP use a new partitioning scheme. It is a complete
	9	replacement for the MSDOS style partitions. It stores its information in a
	10	1MiB journalled database at the end of the physical disk. The size of
	11	partitions is limited only by disk space. The maximum number of partitions is
	12	nearly 2000.
	13
	14	Any partitions created under the LDM are called "Dynamic Disks". There are no
	15	longer any primary or extended partitions. Normal MSDOS style partitions are
	16	now known as Basic Disks.
	17
	18	If you wish to use Spanned, Striped, Mirrored or RAID 5 Volumes, you must use
	19	Dynamic Disks. The journalling allows Windows to make changes to these
	20	partitions and filesystems without the need to reboot.
	21
	22	Once the LDM driver has divided up the disk, you can use the MD driver to
	23	assemble any multi-partition volumes, e.g. Stripes, RAID5.
	24
	25	To prevent legacy applications from repartitioning the disk, the LDM creates a
	26	dummy MSDOS partition containing one disk-sized partition.
	27
	28
	29	Example
	30	-------
	31
	32	Below we have a 50MiB disk, divided into seven partitions.
	33	N.B. The missing 1MiB at the end of the disk is where the LDM database is
	34	stored.
	35
	36	Device \| Offset Bytes Sectors MiB \| Size Bytes Sectors MiB
	37	-------+----------------------------+---------------------------
	38	hda \| 0 0 0 \| 52428800 102400 50
	39	hda1 \| 51380224 100352 49 \| 1048576 2048 1
	40	hda2 \| 16384 32 0 \| 6979584 13632 6
	41	hda3 \| 6995968 13664 6 \| 10485760 20480 10
	42	hda4 \| 17481728 34144 16 \| 4194304 8192 4
	43	hda5 \| 21676032 42336 20 \| 5242880 10240 5
	44	hda6 \| 26918912 52576 25 \| 10485760 20480 10
	45	hda7 \| 37404672 73056 35 \| 13959168 27264 13
	46
	47	The LDM Database may not store the partitions in the order that they appear on
	48	disk, but the driver will sort them.
	49
	50	When Linux boots, you will see something like:
	51
	52	hda: 102400 sectors w/32KiB Cache, CHS=50/64/32
	53	hda: [LDM] hda1 hda2 hda3 hda4 hda5 hda6 hda7
	54
	55
	56	Compiling LDM Support
	57	---------------------
	58
	59	To enable LDM, choose the following two options:
	60
	61	"Advanced partition selection" CONFIG_PARTITION_ADVANCED
	62	"Windows Logical Disk Manager (Dynamic Disk) support" CONFIG_LDM_PARTITION
	63
	64	If you believe the driver isn't working as it should, you can enable the extra
65	debugging code. This will produce a LOT of output. The option is:
66
67	"Windows LDM extra logging" CONFIG_LDM_DEBUG
68
69	N.B. The partition code cannot be compiled as a module.
70
71	As with all the partition code, if the driver doesn't see signs of its type of
72	partition, it will pass control to another driver, so there is no harm in
73	enabling it.
74
75	If you have Dynamic Disks but don't enable the driver, then all you will see
76	is a dummy MSDOS partition filling the whole disk. You won't be able to mount
77	any of the volumes on the disk.
78
79
80	Booting
81	-------
82
83	If you enable LDM support, then lilo is capable of booting from any of the
84	discovered partitions. However, grub does not understand the LDM partitioning
85	and cannot boot from a Dynamic Disk.
86
87
88	More Documentation
89	------------------
90
91	There is an Overview of the LDM online together with complete Technical
92	Documentation. It can also be downloaded in html.
93
94	http://linux-ntfs.sourceforge.net/ldm/index.html
95	http://linux-ntfs.sourceforge.net/downloads.html
96
97	If you have any LDM questions that aren't answered on the website, email me.
98
99	Cheers,
100	FlatCap - Richard Russon
101	ldm@flatcap.org
102