OpenCloudOS-Kernel/Documentation/filesystems/ntfs.rst

.. SPDX-License-Identifier: GPL-2.0

================================
The Linux NTFS filesystem driver
================================


.. Table of contents

   - Overview
   - Web site
   - Features
   - Supported mount options
   - Known bugs and (mis-)features
   - Using NTFS volume and stripe sets
     - The Device-Mapper driver
     - The Software RAID / MD driver
     - Limitations when using the MD driver


Overview
========

Linux-NTFS comes with a number of user-space programs known as ntfsprogs.
These include mkntfs, a full-featured ntfs filesystem format utility,
ntfsundelete used for recovering files that were unintentionally deleted
from an NTFS volume and ntfsresize which is used to resize an NTFS partition.
See the web site for more information.

To mount an NTFS 1.2/3.x (Windows NT4/2000/XP/2003) volume, use the file
system type 'ntfs'.  The driver currently supports read-only mode (with no
fault-tolerance, encryption or journalling) and very limited, but safe, write
support.

For fault tolerance and raid support (i.e. volume and stripe sets), you can
use the kernel's Software RAID / MD driver.  See section "Using Software RAID
with NTFS" for details.


Web site
========

There is plenty of additional information on the linux-ntfs web site
at http://www.linux-ntfs.org/

The web site has a lot of additional information, such as a comprehensive
FAQ, documentation on the NTFS on-disk format, information on the Linux-NTFS
userspace utilities, etc.


Features
========

- This is a complete rewrite of the NTFS driver that used to be in the 2.4 and
  earlier kernels.  This new driver implements NTFS read support and is
  functionally equivalent to the old ntfs driver and it also implements limited
  write support.  The biggest limitation at present is that files/directories
  cannot be created or deleted.  See below for the list of write features that
  are so far supported.  Another limitation is that writing to compressed files
  is not implemented at all.  Also, neither read nor write access to encrypted
  files is so far implemented.
- The new driver has full support for sparse files on NTFS 3.x volumes which
  the old driver isn't happy with.
- The new driver supports execution of binaries due to mmap() now being
  supported.
- The new driver supports loopback mounting of files on NTFS which is used by
  some Linux distributions to enable the user to run Linux from an NTFS
  partition by creating a large file while in Windows and then loopback
  mounting the file while in Linux and creating a Linux filesystem on it that
  is used to install Linux on it.
- A comparison of the two drivers using::

	time find . -type f -exec md5sum "{}" \;

  run three times in sequence with each driver (after a reboot) on a 1.4GiB
  NTFS partition, showed the new driver to be 20% faster in total time elapsed
  (from 9:43 minutes on average down to 7:53).  The time spent in user space
  was unchanged but the time spent in the kernel was decreased by a factor of
  2.5 (from 85 CPU seconds down to 33).
- The driver does not support short file names in general.  For backwards
  compatibility, we implement access to files using their short file names if
  they exist.  The driver will not create short file names however, and a
  rename will discard any existing short file name.
- The new driver supports exporting of mounted NTFS volumes via NFS.
- The new driver supports async io (aio).
- The new driver supports fsync(2), fdatasync(2), and msync(2).
- The new driver supports readv(2) and writev(2).
- The new driver supports access time updates (including mtime and ctime).
- The new driver supports truncate(2) and open(2) with O_TRUNC.  But at present
  only very limited support for highly fragmented files, i.e. ones which have
  their data attribute split across multiple extents, is included.  Another
  limitation is that at present truncate(2) will never create sparse files,
  since to mark a file sparse we need to modify the directory entry for the
  file and we do not implement directory modifications yet.
- The new driver supports write(2) which can both overwrite existing data and
  extend the file size so that you can write beyond the existing data.  Also,
  writing into sparse regions is supported and the holes are filled in with
  clusters.  But at present only limited support for highly fragmented files,
  i.e. ones which have their data attribute split across multiple extents, is
  included.  Another limitation is that write(2) will never create sparse
  files, since to mark a file sparse we need to modify the directory entry for
  the file and we do not implement directory modifications yet.

Supported mount options
=======================

In addition to the generic mount options described by the manual page for the
mount command (man 8 mount, also see man 5 fstab), the NTFS driver supports the
following mount options:

======================= =======================================================
iocharset=name		Deprecated option.  Still supported but please use
			nls=name in the future.  See description for nls=name.

nls=name		Character set to use when returning file names.
			Unlike VFAT, NTFS suppresses names that contain
			unconvertible characters.  Note that most character
			sets contain insufficient characters to represent all
			possible Unicode characters that can exist on NTFS.
			To be sure you are not missing any files, you are
			advised to use nls=utf8 which is capable of
			representing all Unicode characters.

utf8=<bool>		Option no longer supported.  Currently mapped to
			nls=utf8 but please use nls=utf8 in the future and
			make sure utf8 is compiled either as module or into
			the kernel.  See description for nls=name.

uid=
gid=
umask=			Provide default owner, group, and access mode mask.
			These options work as documented in mount(8).  By
			default, the files/directories are owned by root and
			he/she has read and write permissions, as well as
			browse permission for directories.  No one else has any
			access permissions.  I.e. the mode on all files is by
			default rw------- and for directories rwx------, a
			consequence of the default fmask=0177 and dmask=0077.
			Using a umask of zero will grant all permissions to
			everyone, i.e. all files and directories will have mode
			rwxrwxrwx.

fmask=
dmask=			Instead of specifying umask which applies both to
			files and directories, fmask applies only to files and
			dmask only to directories.

sloppy=<BOOL>		If sloppy is specified, ignore unknown mount options.
			Otherwise the default behaviour is to abort mount if
			any unknown options are found.

show_sys_files=<BOOL>	If show_sys_files is specified, show the system files
			in directory listings.  Otherwise the default behaviour
			is to hide the system files.
			Note that even when show_sys_files is specified, "$MFT"
			will not be visible due to bugs/mis-features in glibc.
			Further, note that irrespective of show_sys_files, all
			files are accessible by name, i.e. you can always do
			"ls -l \$UpCase" for example to specifically show the
			system file containing the Unicode upcase table.

case_sensitive=<BOOL>	If case_sensitive is specified, treat all file names as
			case sensitive and create file names in the POSIX
			namespace.  Otherwise the default behaviour is to treat
			file names as case insensitive and to create file names
			in the WIN32/LONG name space.  Note, the Linux NTFS
			driver will never create short file names and will
			remove them on rename/delete of the corresponding long
			file name.
			Note that files remain accessible via their short file
			name, if it exists.  If case_sensitive, you will need
			to provide the correct case of the short file name.

disable_sparse=<BOOL>	If disable_sparse is specified, creation of sparse
			regions, i.e. holes, inside files is disabled for the
			volume (for the duration of this mount only).  By
			default, creation of sparse regions is enabled, which
			is consistent with the behaviour of traditional Unix
			filesystems.

errors=opt		What to do when critical filesystem errors are found.
			Following values can be used for "opt":

			  ========  =========================================
			  continue  DEFAULT, try to clean-up as much as
				    possible, e.g. marking a corrupt inode as
				    bad so it is no longer accessed, and then
				    continue.
			  recover   At present only supported is recovery of
				    the boot sector from the backup copy.
				    If read-only mount, the recovery is done
				    in memory only and not written to disk.
			  ========  =========================================

			Note that the options are additive, i.e. specifying::

			   errors=continue,errors=recover

			means the driver will attempt to recover and if that
			fails it will clean-up as much as possible and
			continue.

mft_zone_multiplier=	Set the MFT zone multiplier for the volume (this
			setting is not persistent across mounts and can be
			changed from mount to mount but cannot be changed on
			remount).  Values of 1 to 4 are allowed, 1 being the
			default.  The MFT zone multiplier determines how much
			space is reserved for the MFT on the volume.  If all
			other space is used up, then the MFT zone will be
			shrunk dynamically, so this has no impact on the
			amount of free space.  However, it can have an impact
			on performance by affecting fragmentation of the MFT.
			In general use the default.  If you have a lot of small
			files then use a higher value.  The values have the
			following meaning:

			      =====	    =================================
			      Value	     MFT zone size (% of volume size)
			      =====	    =================================
				1		12.5%
				2		25%
				3		37.5%
				4		50%
			      =====	    =================================

			Note this option is irrelevant for read-only mounts.
======================= =======================================================


Known bugs and (mis-)features
=============================

- The link count on each directory inode entry is set to 1, due to Linux not
  supporting directory hard links.  This may well confuse some user space
  applications, since the directory names will have the same inode numbers.
  This also speeds up ntfs_read_inode() immensely.  And we haven't found any
  problems with this approach so far.  If you find a problem with this, please
  let us know.


Please send bug reports/comments/feedback/abuse to the Linux-NTFS development
list at sourceforge: linux-ntfs-dev@lists.sourceforge.net


Using NTFS volume and stripe sets
=================================

For support of volume and stripe sets, you can either use the kernel's
Device-Mapper driver or the kernel's Software RAID / MD driver.  The former is
the recommended one to use for linear raid.  But the latter is required for
raid level 5.  For striping and mirroring, either driver should work fine.


The Device-Mapper driver
------------------------

You will need to create a table of the components of the volume/stripe set and
how they fit together and load this into the kernel using the dmsetup utility
(see man 8 dmsetup).

Linear volume sets, i.e. linear raid, has been tested and works fine.  Even
though untested, there is no reason why stripe sets, i.e. raid level 0, and
mirrors, i.e. raid level 1 should not work, too.  Stripes with parity, i.e.
raid level 5, unfortunately cannot work yet because the current version of the
Device-Mapper driver does not support raid level 5.  You may be able to use the
Software RAID / MD driver for raid level 5, see the next section for details.

To create the table describing your volume you will need to know each of its
components and their sizes in sectors, i.e. multiples of 512-byte blocks.

For NT4 fault tolerant volumes you can obtain the sizes using fdisk.  So for
example if one of your partitions is /dev/hda2 you would do::

    $ fdisk -ul /dev/hda

    Disk /dev/hda: 81.9 GB, 81964302336 bytes
    255 heads, 63 sectors/track, 9964 cylinders, total 160086528 sectors
    Units = sectors of 1 * 512 = 512 bytes

	Device Boot      Start         End      Blocks   Id  System
	/dev/hda1   *          63     4209029     2104483+  83  Linux
	/dev/hda2         4209030    37768814    16779892+  86  NTFS
	/dev/hda3        37768815    46170809     4200997+  83  Linux

And you would know that /dev/hda2 has a size of 37768814 - 4209030 + 1 =
33559785 sectors.

For Win2k and later dynamic disks, you can for example use the ldminfo utility
which is part of the Linux LDM tools (the latest version at the time of
writing is linux-ldm-0.0.8.tar.bz2).  You can download it from:

	http://www.linux-ntfs.org/

Simply extract the downloaded archive (tar xvjf linux-ldm-0.0.8.tar.bz2), go
into it (cd linux-ldm-0.0.8) and change to the test directory (cd test).  You
will find the precompiled (i386) ldminfo utility there.  NOTE: You will not be
able to compile this yourself easily so use the binary version!

Then you would use ldminfo in dump mode to obtain the necessary information::

    $ ./ldminfo --dump /dev/hda

This would dump the LDM database found on /dev/hda which describes all of your
dynamic disks and all the volumes on them.  At the bottom you will see the
VOLUME DEFINITIONS section which is all you really need.  You may need to look
further above to determine which of the disks in the volume definitions is
which device in Linux.  Hint: Run ldminfo on each of your dynamic disks and
look at the Disk Id close to the top of the output for each (the PRIVATE HEADER
section).  You can then find these Disk Ids in the VBLK DATABASE section in the
<Disk> components where you will get the LDM Name for the disk that is found in
the VOLUME DEFINITIONS section.

Note you will also need to enable the LDM driver in the Linux kernel.  If your
distribution did not enable it, you will need to recompile the kernel with it
enabled.  This will create the LDM partitions on each device at boot time.  You
would then use those devices (for /dev/hda they would be /dev/hda1, 2, 3, etc)
in the Device-Mapper table.

You can also bypass using the LDM driver by using the main device (e.g.
/dev/hda) and then using the offsets of the LDM partitions into this device as
the "Start sector of device" when creating the table.  Once again ldminfo would
give you the correct information to do this.

Assuming you know all your devices and their sizes things are easy.

For a linear raid the table would look like this (note all values are in
512-byte sectors)::

    # Offset into	Size of this	Raid type	Device		Start sector
    # volume	device						of device
    0		1028161		linear		/dev/hda1	0
    1028161		3903762		linear		/dev/hdb2	0
    4931923		2103211		linear		/dev/hdc1	0

For a striped volume, i.e. raid level 0, you will need to know the chunk size
you used when creating the volume.  Windows uses 64kiB as the default, so it
will probably be this unless you changes the defaults when creating the array.

For a raid level 0 the table would look like this (note all values are in
512-byte sectors)::

    # Offset   Size	    Raid     Number   Chunk  1st        Start	2nd	  Start
    # into     of the   type     of	      size   Device	in	Device	  in
    # volume   volume	     stripes			device		  device
    0	   2056320  striped  2	      128    /dev/hda1	0	/dev/hdb1 0

If there are more than two devices, just add each of them to the end of the
line.

Finally, for a mirrored volume, i.e. raid level 1, the table would look like
this (note all values are in 512-byte sectors)::

    # Ofs Size   Raid   Log  Number Region Should Number Source  Start Target Start
    # in  of the type   type of log size   sync?  of     Device  in    Device in
    # vol volume		 params		     mirrors	     Device	  Device
    0    2056320 mirror core 2	16     nosync 2	   /dev/hda1 0   /dev/hdb1 0

If you are mirroring to multiple devices you can specify further targets at the
end of the line.

Note the "Should sync?" parameter "nosync" means that the two mirrors are
already in sync which will be the case on a clean shutdown of Windows.  If the
mirrors are not clean, you can specify the "sync" option instead of "nosync"
and the Device-Mapper driver will then copy the entirety of the "Source Device"
to the "Target Device" or if you specified multiple target devices to all of
them.

Once you have your table, save it in a file somewhere (e.g. /etc/ntfsvolume1),
and hand it over to dmsetup to work with, like so::

    $ dmsetup create myvolume1 /etc/ntfsvolume1

You can obviously replace "myvolume1" with whatever name you like.

If it all worked, you will now have the device /dev/device-mapper/myvolume1
which you can then just use as an argument to the mount command as usual to
mount the ntfs volume.  For example::

    $ mount -t ntfs -o ro /dev/device-mapper/myvolume1 /mnt/myvol1

(You need to create the directory /mnt/myvol1 first and of course you can use
anything you like instead of /mnt/myvol1 as long as it is an existing
directory.)

It is advisable to do the mount read-only to see if the volume has been setup
correctly to avoid the possibility of causing damage to the data on the ntfs
volume.


The Software RAID / MD driver
-----------------------------

An alternative to using the Device-Mapper driver is to use the kernel's
Software RAID / MD driver.  For which you need to set up your /etc/raidtab
appropriately (see man 5 raidtab).

Linear volume sets, i.e. linear raid, as well as stripe sets, i.e. raid level
0, have been tested and work fine (though see section "Limitations when using
the MD driver with NTFS volumes" especially if you want to use linear raid).
Even though untested, there is no reason why mirrors, i.e. raid level 1, and
stripes with parity, i.e. raid level 5, should not work, too.

You have to use the "persistent-superblock 0" option for each raid-disk in the
NTFS volume/stripe you are configuring in /etc/raidtab as the persistent
superblock used by the MD driver would damage the NTFS volume.

Windows by default uses a stripe chunk size of 64k, so you probably want the
"chunk-size 64k" option for each raid-disk, too.

For example, if you have a stripe set consisting of two partitions /dev/hda5
and /dev/hdb1 your /etc/raidtab would look like this::

    raiddev /dev/md0
	    raid-level	0
	    nr-raid-disks	2
	    nr-spare-disks	0
	    persistent-superblock	0
	    chunk-size	64k
	    device		/dev/hda5
	    raid-disk	0
	    device		/dev/hdb1
	    raid-disk	1

For linear raid, just change the raid-level above to "raid-level linear", for
mirrors, change it to "raid-level 1", and for stripe sets with parity, change
it to "raid-level 5".

Note for stripe sets with parity you will also need to tell the MD driver
which parity algorithm to use by specifying the option "parity-algorithm
which", where you need to replace "which" with the name of the algorithm to
use (see man 5 raidtab for available algorithms) and you will have to try the
different available algorithms until you find one that works.  Make sure you
are working read-only when playing with this as you may damage your data
otherwise.  If you find which algorithm works please let us know (email the
linux-ntfs developers list linux-ntfs-dev@lists.sourceforge.net or drop in on
IRC in channel #ntfs on the irc.freenode.net network) so we can update this
documentation.

Once the raidtab is setup, run for example raid0run -a to start all devices or
raid0run /dev/md0 to start a particular md device, in this case /dev/md0.

Then just use the mount command as usual to mount the ntfs volume using for
example::

    mount -t ntfs -o ro /dev/md0 /mnt/myntfsvolume

It is advisable to do the mount read-only to see if the md volume has been
setup correctly to avoid the possibility of causing damage to the data on the
ntfs volume.


Limitations when using the Software RAID / MD driver
-----------------------------------------------------

Using the md driver will not work properly if any of your NTFS partitions have
an odd number of sectors.  This is especially important for linear raid as all
data after the first partition with an odd number of sectors will be offset by
one or more sectors so if you mount such a partition with write support you
will cause massive damage to the data on the volume which will only become
apparent when you try to use the volume again under Windows.

So when using linear raid, make sure that all your partitions have an even
number of sectors BEFORE attempting to use it.  You have been warned!

Even better is to simply use the Device-Mapper for linear raid and then you do
not have this problem with odd numbers of sectors.