110 lines
3.9 KiB
Plaintext
110 lines
3.9 KiB
Plaintext
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LDM - Logical Disk Manager (Dynamic Disks)
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------------------------------------------
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Originally Written by FlatCap - Richard Russon <ldm@flatcap.org>.
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Last Updated by Anton Altaparmakov on 30 March 2007 for Windows Vista.
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Overview
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--------
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Windows 2000, XP, and Vista use a new partitioning scheme. It is a complete
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replacement for the MSDOS style partitions. It stores its information in a
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1MiB journalled database at the end of the physical disk. The size of
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partitions is limited only by disk space. The maximum number of partitions is
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nearly 2000.
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Any partitions created under the LDM are called "Dynamic Disks". There are no
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longer any primary or extended partitions. Normal MSDOS style partitions are
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now known as Basic Disks.
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If you wish to use Spanned, Striped, Mirrored or RAID 5 Volumes, you must use
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Dynamic Disks. The journalling allows Windows to make changes to these
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partitions and filesystems without the need to reboot.
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Once the LDM driver has divided up the disk, you can use the MD driver to
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assemble any multi-partition volumes, e.g. Stripes, RAID5.
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To prevent legacy applications from repartitioning the disk, the LDM creates a
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dummy MSDOS partition containing one disk-sized partition. This is what is
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supported with the Linux LDM driver.
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A newer approach that has been implemented with Vista is to put LDM on top of a
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GPT label disk. This is not supported by the Linux LDM driver yet.
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Example
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-------
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Below we have a 50MiB disk, divided into seven partitions.
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N.B. The missing 1MiB at the end of the disk is where the LDM database is
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stored.
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Device | Offset Bytes Sectors MiB | Size Bytes Sectors MiB
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-------+----------------------------+---------------------------
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hda | 0 0 0 | 52428800 102400 50
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hda1 | 51380224 100352 49 | 1048576 2048 1
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hda2 | 16384 32 0 | 6979584 13632 6
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hda3 | 6995968 13664 6 | 10485760 20480 10
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hda4 | 17481728 34144 16 | 4194304 8192 4
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hda5 | 21676032 42336 20 | 5242880 10240 5
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hda6 | 26918912 52576 25 | 10485760 20480 10
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hda7 | 37404672 73056 35 | 13959168 27264 13
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The LDM Database may not store the partitions in the order that they appear on
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disk, but the driver will sort them.
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When Linux boots, you will see something like:
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hda: 102400 sectors w/32KiB Cache, CHS=50/64/32
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hda: [LDM] hda1 hda2 hda3 hda4 hda5 hda6 hda7
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Compiling LDM Support
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---------------------
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To enable LDM, choose the following two options:
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"Advanced partition selection" CONFIG_PARTITION_ADVANCED
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"Windows Logical Disk Manager (Dynamic Disk) support" CONFIG_LDM_PARTITION
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If you believe the driver isn't working as it should, you can enable the extra
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debugging code. This will produce a LOT of output. The option is:
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"Windows LDM extra logging" CONFIG_LDM_DEBUG
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N.B. The partition code cannot be compiled as a module.
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As with all the partition code, if the driver doesn't see signs of its type of
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partition, it will pass control to another driver, so there is no harm in
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enabling it.
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If you have Dynamic Disks but don't enable the driver, then all you will see
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is a dummy MSDOS partition filling the whole disk. You won't be able to mount
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any of the volumes on the disk.
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Booting
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-------
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If you enable LDM support, then lilo is capable of booting from any of the
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discovered partitions. However, grub does not understand the LDM partitioning
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and cannot boot from a Dynamic Disk.
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More Documentation
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------------------
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There is an Overview of the LDM together with complete Technical Documentation.
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It is available for download.
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http://www.linux-ntfs.org/content/view/19/37/
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If you have any LDM questions that aren't answered in the documentation, email
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me.
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Cheers,
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FlatCap - Richard Russon
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ldm@flatcap.org
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