Documentation/ldm.txt

   1 ==========================================
   2 LDM - Logical Disk Manager (Dynamic Disks)
   3 ==========================================
   4
   5 :Author: Originally Written by FlatCap - Richard Russon <ldm@flatcap.org>.
   6 :Last Updated: Anton Altaparmakov on 30 March 2007 for Windows Vista.
   7
   8 Overview
   9 --------
  10
  11 Windows 2000, XP, and Vista use a new partitioning scheme.  It is a complete
  12 replacement for the MSDOS style partitions.  It stores its information in a
  13 1MiB journalled database at the end of the physical disk.  The size of
  14 partitions is limited only by disk space.  The maximum number of partitions is
  15 nearly 2000.
  16
  17 Any partitions created under the LDM are called "Dynamic Disks".  There are no
  18 longer any primary or extended partitions.  Normal MSDOS style partitions are
  19 now known as Basic Disks.
  20
  21 If you wish to use Spanned, Striped, Mirrored or RAID 5 Volumes, you must use
  22 Dynamic Disks.  The journalling allows Windows to make changes to these
  23 partitions and filesystems without the need to reboot.
  24
  25 Once the LDM driver has divided up the disk, you can use the MD driver to
  26 assemble any multi-partition volumes, e.g.  Stripes, RAID5.
  27
  28 To prevent legacy applications from repartitioning the disk, the LDM creates a
  29 dummy MSDOS partition containing one disk-sized partition.  This is what is
  30 supported with the Linux LDM driver.
  31
  32 A newer approach that has been implemented with Vista is to put LDM on top of a
  33 GPT label disk.  This is not supported by the Linux LDM driver yet.
  34
  35
  36 Example
  37 -------
  38
  39 Below we have a 50MiB disk, divided into seven partitions.
  40
  41 .. note::
  42
  43    The missing 1MiB at the end of the disk is where the LDM database is
  44    stored.
  45
  46 +-------++--------------+---------+-----++--------------+---------+----+
  47 |Device || Offset Bytes | Sectors | MiB || Size   Bytes | Sectors | MiB|
  48 +=======++==============+=========+=====++==============+=========+====+
  49 |hda    ||            0 |       0 |   0 ||     52428800 |  102400 |  50|
  50 +-------++--------------+---------+-----++--------------+---------+----+
  51 |hda1   ||     51380224 |  100352 |  49 ||      1048576 |    2048 |   1|
  52 +-------++--------------+---------+-----++--------------+---------+----+
  53 |hda2   ||        16384 |      32 |   0 ||      6979584 |   13632 |   6|
  54 +-------++--------------+---------+-----++--------------+---------+----+
  55 |hda3   ||      6995968 |   13664 |   6 ||     10485760 |   20480 |  10|
  56 +-------++--------------+---------+-----++--------------+---------+----+
  57 |hda4   ||     17481728 |   34144 |  16 ||      4194304 |    8192 |   4|
  58 +-------++--------------+---------+-----++--------------+---------+----+
  59 |hda5   ||     21676032 |   42336 |  20 ||      5242880 |   10240 |   5|
  60 +-------++--------------+---------+-----++--------------+---------+----+
  61 |hda6   ||     26918912 |   52576 |  25 ||     10485760 |   20480 |  10|
  62 +-------++--------------+---------+-----++--------------+---------+----+
  63 |hda7   ||     37404672 |   73056 |  35 ||     13959168 |   27264 |  13|
  64 +-------++--------------+---------+-----++--------------+---------+----+
  65
  66 The LDM Database may not store the partitions in the order that they appear on
  67 disk, but the driver will sort them.
  68
  69 When Linux boots, you will see something like::
  70
  71   hda: 102400 sectors w/32KiB Cache, CHS=50/64/32
  72   hda: [LDM] hda1 hda2 hda3 hda4 hda5 hda6 hda7
  73
  74
  75 Compiling LDM Support
  76 ---------------------
  77
  78 To enable LDM, choose the following two options:
  79
  80   - "Advanced partition selection" CONFIG_PARTITION_ADVANCED
  81   - "Windows Logical Disk Manager (Dynamic Disk) support" CONFIG_LDM_PARTITION
  82
  83 If you believe the driver isn't working as it should, you can enable the extra
  84 debugging code.  This will produce a LOT of output.  The option is:
  85
  86   - "Windows LDM extra logging" CONFIG_LDM_DEBUG
  87
  88 N.B. The partition code cannot be compiled as a module.
  89
  90 As with all the partition code, if the driver doesn't see signs of its type of
  91 partition, it will pass control to another driver, so there is no harm in
  92 enabling it.
  93
  94 If you have Dynamic Disks but don't enable the driver, then all you will see
  95 is a dummy MSDOS partition filling the whole disk.  You won't be able to mount
  96 any of the volumes on the disk.
  97
  98
  99 Booting
 100 -------
 101
 102 If you enable LDM support, then lilo is capable of booting from any of the
 103 discovered partitions.  However, grub does not understand the LDM partitioning
 104 and cannot boot from a Dynamic Disk.
 105
 106
 107 More Documentation
 108 ------------------
 109
 110 There is an Overview of the LDM together with complete Technical Documentation.
 111 It is available for download.
 112
 113   http://www.linux-ntfs.org/
 114
 115 If you have any LDM questions that aren't answered in the documentation, email
 116 me.
 117
 118 Cheers,
 119     FlatCap - Richard Russon
 120     ldm@flatcap.org
 121