/Documentation/ldm.txt

  1
  2            LDM - Logical Disk Manager (Dynamic Disks)
  3            ------------------------------------------
  4
  5Originally Written by FlatCap - Richard Russon <ldm@flatcap.org>.
  6Last Updated by Anton Altaparmakov on 30 March 2007 for Windows Vista.
  7
  8Overview
  9--------
 10
 11Windows 2000, XP, and Vista use a new partitioning scheme.  It is a complete
 12replacement for the MSDOS style partitions.  It stores its information in a
 131MiB journalled database at the end of the physical disk.  The size of
 14partitions is limited only by disk space.  The maximum number of partitions is
 15nearly 2000.
 16
 17Any partitions created under the LDM are called "Dynamic Disks".  There are no
 18longer any primary or extended partitions.  Normal MSDOS style partitions are
 19now known as Basic Disks.
 20
 21If you wish to use Spanned, Striped, Mirrored or RAID 5 Volumes, you must use
 22Dynamic Disks.  The journalling allows Windows to make changes to these
 23partitions and filesystems without the need to reboot.
 24
 25Once the LDM driver has divided up the disk, you can use the MD driver to
 26assemble any multi-partition volumes, e.g.  Stripes, RAID5.
 27
 28To prevent legacy applications from repartitioning the disk, the LDM creates a
 29dummy MSDOS partition containing one disk-sized partition.  This is what is
 30supported with the Linux LDM driver.
 31
 32A newer approach that has been implemented with Vista is to put LDM on top of a
 33GPT label disk.  This is not supported by the Linux LDM driver yet.
 34
 35
 36Example
 37-------
 38
 39Below we have a 50MiB disk, divided into seven partitions.
 40N.B.  The missing 1MiB at the end of the disk is where the LDM database is
 41      stored.
 42
 43  Device | Offset Bytes  Sectors  MiB | Size   Bytes  Sectors  MiB
 44  -------+----------------------------+---------------------------
 45  hda    |            0        0    0 |     52428800   102400   50
 46  hda1   |     51380224   100352   49 |      1048576     2048    1
 47  hda2   |        16384       32    0 |      6979584    13632    6
 48  hda3   |      6995968    13664    6 |     10485760    20480   10
 49  hda4   |     17481728    34144   16 |      4194304     8192    4
 50  hda5   |     21676032    42336   20 |      5242880    10240    5
 51  hda6   |     26918912    52576   25 |     10485760    20480   10
 52  hda7   |     37404672    73056   35 |     13959168    27264   13
 53
 54The LDM Database may not store the partitions in the order that they appear on
 55disk, but the driver will sort them.
 56
 57When Linux boots, you will see something like:
 58
 59  hda: 102400 sectors w/32KiB Cache, CHS=50/64/32
 60  hda: [LDM] hda1 hda2 hda3 hda4 hda5 hda6 hda7
 61
 62
 63Compiling LDM Support
 64---------------------
 65
 66To enable LDM, choose the following two options: 
 67
 68  "Advanced partition selection" CONFIG_PARTITION_ADVANCED
 69  "Windows Logical Disk Manager (Dynamic Disk) support" CONFIG_LDM_PARTITION
 70
 71If you believe the driver isn't working as it should, you can enable the extra
 72debugging code.  This will produce a LOT of output.  The option is:
 73
 74  "Windows LDM extra logging" CONFIG_LDM_DEBUG
 75
 76N.B. The partition code cannot be compiled as a module.
 77
 78As with all the partition code, if the driver doesn't see signs of its type of
 79partition, it will pass control to another driver, so there is no harm in
 80enabling it.
 81
 82If you have Dynamic Disks but don't enable the driver, then all you will see
 83is a dummy MSDOS partition filling the whole disk.  You won't be able to mount
 84any of the volumes on the disk.
 85
 86
 87Booting
 88-------
 89
 90If you enable LDM support, then lilo is capable of booting from any of the
 91discovered partitions.  However, grub does not understand the LDM partitioning
 92and cannot boot from a Dynamic Disk.
 93
 94
 95More Documentation
 96------------------
 97
 98There is an Overview of the LDM together with complete Technical Documentation.
 99It is available for download.
100
101  http://www.linux-ntfs.org/content/view/19/37/
102
103If you have any LDM questions that aren't answered in the documentation, email
104me.
105
106Cheers,
107    FlatCap - Richard Russon
108    ldm@flatcap.org
109