About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / filesystems / ntfs.txt

Custom Search

Based on kernel version 3.19. Page generated on 2015-02-13 21:20 EST.

1	The Linux NTFS filesystem driver
2	================================
5	Table of contents
6	=================
8	- Overview
9	- Web site
10	- Features
11	- Supported mount options
12	- Known bugs and (mis-)features
13	- Using NTFS volume and stripe sets
14	  - The Device-Mapper driver
15	  - The Software RAID / MD driver
16	  - Limitations when using the MD driver
19	Overview
20	========
22	Linux-NTFS comes with a number of user-space programs known as ntfsprogs.
23	These include mkntfs, a full-featured ntfs filesystem format utility,
24	ntfsundelete used for recovering files that were unintentionally deleted
25	from an NTFS volume and ntfsresize which is used to resize an NTFS partition.
26	See the web site for more information.
28	To mount an NTFS 1.2/3.x (Windows NT4/2000/XP/2003) volume, use the file
29	system type 'ntfs'.  The driver currently supports read-only mode (with no
30	fault-tolerance, encryption or journalling) and very limited, but safe, write
31	support.
33	For fault tolerance and raid support (i.e. volume and stripe sets), you can
34	use the kernel's Software RAID / MD driver.  See section "Using Software RAID
35	with NTFS" for details.
38	Web site
39	========
41	There is plenty of additional information on the linux-ntfs web site
42	at http://www.linux-ntfs.org/
44	The web site has a lot of additional information, such as a comprehensive
45	FAQ, documentation on the NTFS on-disk format, information on the Linux-NTFS
46	userspace utilities, etc.
49	Features
50	========
52	- This is a complete rewrite of the NTFS driver that used to be in the 2.4 and
53	  earlier kernels.  This new driver implements NTFS read support and is
54	  functionally equivalent to the old ntfs driver and it also implements limited
55	  write support.  The biggest limitation at present is that files/directories
56	  cannot be created or deleted.  See below for the list of write features that
57	  are so far supported.  Another limitation is that writing to compressed files
58	  is not implemented at all.  Also, neither read nor write access to encrypted
59	  files is so far implemented.
60	- The new driver has full support for sparse files on NTFS 3.x volumes which
61	  the old driver isn't happy with.
62	- The new driver supports execution of binaries due to mmap() now being
63	  supported.
64	- The new driver supports loopback mounting of files on NTFS which is used by
65	  some Linux distributions to enable the user to run Linux from an NTFS
66	  partition by creating a large file while in Windows and then loopback
67	  mounting the file while in Linux and creating a Linux filesystem on it that
68	  is used to install Linux on it.
69	- A comparison of the two drivers using:
70		time find . -type f -exec md5sum "{}" \;
71	  run three times in sequence with each driver (after a reboot) on a 1.4GiB
72	  NTFS partition, showed the new driver to be 20% faster in total time elapsed
73	  (from 9:43 minutes on average down to 7:53).  The time spent in user space
74	  was unchanged but the time spent in the kernel was decreased by a factor of
75	  2.5 (from 85 CPU seconds down to 33).
76	- The driver does not support short file names in general.  For backwards
77	  compatibility, we implement access to files using their short file names if
78	  they exist.  The driver will not create short file names however, and a
79	  rename will discard any existing short file name.
80	- The new driver supports exporting of mounted NTFS volumes via NFS.
81	- The new driver supports async io (aio).
82	- The new driver supports fsync(2), fdatasync(2), and msync(2).
83	- The new driver supports readv(2) and writev(2).
84	- The new driver supports access time updates (including mtime and ctime).
85	- The new driver supports truncate(2) and open(2) with O_TRUNC.  But at present
86	  only very limited support for highly fragmented files, i.e. ones which have
87	  their data attribute split across multiple extents, is included.  Another
88	  limitation is that at present truncate(2) will never create sparse files,
89	  since to mark a file sparse we need to modify the directory entry for the
90	  file and we do not implement directory modifications yet.
91	- The new driver supports write(2) which can both overwrite existing data and
92	  extend the file size so that you can write beyond the existing data.  Also,
93	  writing into sparse regions is supported and the holes are filled in with
94	  clusters.  But at present only limited support for highly fragmented files,
95	  i.e. ones which have their data attribute split across multiple extents, is
96	  included.  Another limitation is that write(2) will never create sparse
97	  files, since to mark a file sparse we need to modify the directory entry for
98	  the file and we do not implement directory modifications yet.
100	Supported mount options
101	=======================
103	In addition to the generic mount options described by the manual page for the
104	mount command (man 8 mount, also see man 5 fstab), the NTFS driver supports the
105	following mount options:
107	iocharset=name		Deprecated option.  Still supported but please use
108				nls=name in the future.  See description for nls=name.
110	nls=name		Character set to use when returning file names.
111				Unlike VFAT, NTFS suppresses names that contain
112				unconvertible characters.  Note that most character
113				sets contain insufficient characters to represent all
114				possible Unicode characters that can exist on NTFS.
115				To be sure you are not missing any files, you are
116				advised to use nls=utf8 which is capable of
117				representing all Unicode characters.
119	utf8=<bool>		Option no longer supported.  Currently mapped to
120				nls=utf8 but please use nls=utf8 in the future and
121				make sure utf8 is compiled either as module or into
122				the kernel.  See description for nls=name.
124	uid=
125	gid=
126	umask=			Provide default owner, group, and access mode mask.
127				These options work as documented in mount(8).  By
128				default, the files/directories are owned by root and
129				he/she has read and write permissions, as well as
130				browse permission for directories.  No one else has any
131				access permissions.  I.e. the mode on all files is by
132				default rw------- and for directories rwx------, a
133				consequence of the default fmask=0177 and dmask=0077.
134				Using a umask of zero will grant all permissions to
135				everyone, i.e. all files and directories will have mode
136				rwxrwxrwx.
138	fmask=
139	dmask=			Instead of specifying umask which applies both to
140				files and directories, fmask applies only to files and
141				dmask only to directories.
143	sloppy=<BOOL>		If sloppy is specified, ignore unknown mount options.
144				Otherwise the default behaviour is to abort mount if
145				any unknown options are found.
147	show_sys_files=<BOOL>	If show_sys_files is specified, show the system files
148				in directory listings.  Otherwise the default behaviour
149				is to hide the system files.
150				Note that even when show_sys_files is specified, "$MFT"
151				will not be visible due to bugs/mis-features in glibc.
152				Further, note that irrespective of show_sys_files, all
153				files are accessible by name, i.e. you can always do
154				"ls -l \$UpCase" for example to specifically show the
155				system file containing the Unicode upcase table.
157	case_sensitive=<BOOL>	If case_sensitive is specified, treat all file names as
158				case sensitive and create file names in the POSIX
159				namespace.  Otherwise the default behaviour is to treat
160				file names as case insensitive and to create file names
161				in the WIN32/LONG name space.  Note, the Linux NTFS
162				driver will never create short file names and will
163				remove them on rename/delete of the corresponding long
164				file name.
165				Note that files remain accessible via their short file
166				name, if it exists.  If case_sensitive, you will need
167				to provide the correct case of the short file name.
169	disable_sparse=<BOOL>	If disable_sparse is specified, creation of sparse
170				regions, i.e. holes, inside files is disabled for the
171				volume (for the duration of this mount only).  By
172				default, creation of sparse regions is enabled, which
173				is consistent with the behaviour of traditional Unix
174				filesystems.
176	errors=opt		What to do when critical filesystem errors are found.
177				Following values can be used for "opt":
178				  continue: DEFAULT, try to clean-up as much as
179					    possible, e.g. marking a corrupt inode as
180					    bad so it is no longer accessed, and then
181					    continue.
182				  recover:  At present only supported is recovery of
183					    the boot sector from the backup copy.
184					    If read-only mount, the recovery is done
185					    in memory only and not written to disk.
186				Note that the options are additive, i.e. specifying:
187				   errors=continue,errors=recover
188				means the driver will attempt to recover and if that
189				fails it will clean-up as much as possible and
190				continue.
192	mft_zone_multiplier=	Set the MFT zone multiplier for the volume (this
193				setting is not persistent across mounts and can be
194				changed from mount to mount but cannot be changed on
195				remount).  Values of 1 to 4 are allowed, 1 being the
196				default.  The MFT zone multiplier determines how much
197				space is reserved for the MFT on the volume.  If all
198				other space is used up, then the MFT zone will be
199				shrunk dynamically, so this has no impact on the
200				amount of free space.  However, it can have an impact
201				on performance by affecting fragmentation of the MFT.
202				In general use the default.  If you have a lot of small
203				files then use a higher value.  The values have the
204				following meaning:
205				      Value	     MFT zone size (% of volume size)
206					1		12.5%
207					2		25%
208					3		37.5%
209					4		50%
210				Note this option is irrelevant for read-only mounts.
213	Known bugs and (mis-)features
214	=============================
216	- The link count on each directory inode entry is set to 1, due to Linux not
217	  supporting directory hard links.  This may well confuse some user space
218	  applications, since the directory names will have the same inode numbers.
219	  This also speeds up ntfs_read_inode() immensely.  And we haven't found any
220	  problems with this approach so far.  If you find a problem with this, please
221	  let us know.
224	Please send bug reports/comments/feedback/abuse to the Linux-NTFS development
225	list at sourceforge: linux-ntfs-dev@lists.sourceforge.net
228	Using NTFS volume and stripe sets
229	=================================
231	For support of volume and stripe sets, you can either use the kernel's
232	Device-Mapper driver or the kernel's Software RAID / MD driver.  The former is
233	the recommended one to use for linear raid.  But the latter is required for
234	raid level 5.  For striping and mirroring, either driver should work fine.
237	The Device-Mapper driver
238	------------------------
240	You will need to create a table of the components of the volume/stripe set and
241	how they fit together and load this into the kernel using the dmsetup utility
242	(see man 8 dmsetup).
244	Linear volume sets, i.e. linear raid, has been tested and works fine.  Even
245	though untested, there is no reason why stripe sets, i.e. raid level 0, and
246	mirrors, i.e. raid level 1 should not work, too.  Stripes with parity, i.e.
247	raid level 5, unfortunately cannot work yet because the current version of the
248	Device-Mapper driver does not support raid level 5.  You may be able to use the
249	Software RAID / MD driver for raid level 5, see the next section for details.
251	To create the table describing your volume you will need to know each of its
252	components and their sizes in sectors, i.e. multiples of 512-byte blocks.
254	For NT4 fault tolerant volumes you can obtain the sizes using fdisk.  So for
255	example if one of your partitions is /dev/hda2 you would do:
257	$ fdisk -ul /dev/hda
259	Disk /dev/hda: 81.9 GB, 81964302336 bytes
260	255 heads, 63 sectors/track, 9964 cylinders, total 160086528 sectors
261	Units = sectors of 1 * 512 = 512 bytes
263	   Device Boot      Start         End      Blocks   Id  System
264	   /dev/hda1   *          63     4209029     2104483+  83  Linux
265	   /dev/hda2         4209030    37768814    16779892+  86  NTFS
266	   /dev/hda3        37768815    46170809     4200997+  83  Linux
268	And you would know that /dev/hda2 has a size of 37768814 - 4209030 + 1 =
269	33559785 sectors.
271	For Win2k and later dynamic disks, you can for example use the ldminfo utility
272	which is part of the Linux LDM tools (the latest version at the time of
273	writing is linux-ldm-0.0.8.tar.bz2).  You can download it from:
274		http://www.linux-ntfs.org/
275	Simply extract the downloaded archive (tar xvjf linux-ldm-0.0.8.tar.bz2), go
276	into it (cd linux-ldm-0.0.8) and change to the test directory (cd test).  You
277	will find the precompiled (i386) ldminfo utility there.  NOTE: You will not be
278	able to compile this yourself easily so use the binary version!
280	Then you would use ldminfo in dump mode to obtain the necessary information:
282	$ ./ldminfo --dump /dev/hda
284	This would dump the LDM database found on /dev/hda which describes all of your
285	dynamic disks and all the volumes on them.  At the bottom you will see the
286	VOLUME DEFINITIONS section which is all you really need.  You may need to look
287	further above to determine which of the disks in the volume definitions is
288	which device in Linux.  Hint: Run ldminfo on each of your dynamic disks and
289	look at the Disk Id close to the top of the output for each (the PRIVATE HEADER
290	section).  You can then find these Disk Ids in the VBLK DATABASE section in the
291	<Disk> components where you will get the LDM Name for the disk that is found in
292	the VOLUME DEFINITIONS section.
294	Note you will also need to enable the LDM driver in the Linux kernel.  If your
295	distribution did not enable it, you will need to recompile the kernel with it
296	enabled.  This will create the LDM partitions on each device at boot time.  You
297	would then use those devices (for /dev/hda they would be /dev/hda1, 2, 3, etc)
298	in the Device-Mapper table.
300	You can also bypass using the LDM driver by using the main device (e.g.
301	/dev/hda) and then using the offsets of the LDM partitions into this device as
302	the "Start sector of device" when creating the table.  Once again ldminfo would
303	give you the correct information to do this.
305	Assuming you know all your devices and their sizes things are easy.
307	For a linear raid the table would look like this (note all values are in
308	512-byte sectors):
310	--- cut here ---
311	# Offset into	Size of this	Raid type	Device		Start sector
312	# volume	device						of device
313	0		1028161		linear		/dev/hda1	0
314	1028161		3903762		linear		/dev/hdb2	0
315	4931923		2103211		linear		/dev/hdc1	0
316	--- cut here ---
318	For a striped volume, i.e. raid level 0, you will need to know the chunk size
319	you used when creating the volume.  Windows uses 64kiB as the default, so it
320	will probably be this unless you changes the defaults when creating the array.
322	For a raid level 0 the table would look like this (note all values are in
323	512-byte sectors):
325	--- cut here ---
326	# Offset   Size	    Raid     Number   Chunk  1st        Start	2nd	  Start
327	# into     of the   type     of	      size   Device	in	Device	  in
328	# volume   volume	     stripes			device		  device
329	0	   2056320  striped  2	      128    /dev/hda1	0	/dev/hdb1 0
330	--- cut here ---
332	If there are more than two devices, just add each of them to the end of the
333	line.
335	Finally, for a mirrored volume, i.e. raid level 1, the table would look like
336	this (note all values are in 512-byte sectors):
338	--- cut here ---
339	# Ofs Size   Raid   Log  Number Region Should Number Source  Start Target Start
340	# in  of the type   type of log size   sync?  of     Device  in    Device in
341	# vol volume		 params		     mirrors	     Device	  Device
342	0    2056320 mirror core 2	16     nosync 2	   /dev/hda1 0   /dev/hdb1 0
343	--- cut here ---
345	If you are mirroring to multiple devices you can specify further targets at the
346	end of the line.
348	Note the "Should sync?" parameter "nosync" means that the two mirrors are
349	already in sync which will be the case on a clean shutdown of Windows.  If the
350	mirrors are not clean, you can specify the "sync" option instead of "nosync"
351	and the Device-Mapper driver will then copy the entirety of the "Source Device"
352	to the "Target Device" or if you specified multiple target devices to all of
353	them.
355	Once you have your table, save it in a file somewhere (e.g. /etc/ntfsvolume1),
356	and hand it over to dmsetup to work with, like so:
358	$ dmsetup create myvolume1 /etc/ntfsvolume1
360	You can obviously replace "myvolume1" with whatever name you like.
362	If it all worked, you will now have the device /dev/device-mapper/myvolume1
363	which you can then just use as an argument to the mount command as usual to
364	mount the ntfs volume.  For example:
366	$ mount -t ntfs -o ro /dev/device-mapper/myvolume1 /mnt/myvol1
368	(You need to create the directory /mnt/myvol1 first and of course you can use
369	anything you like instead of /mnt/myvol1 as long as it is an existing
370	directory.)
372	It is advisable to do the mount read-only to see if the volume has been setup
373	correctly to avoid the possibility of causing damage to the data on the ntfs
374	volume.
377	The Software RAID / MD driver
378	-----------------------------
380	An alternative to using the Device-Mapper driver is to use the kernel's
381	Software RAID / MD driver.  For which you need to set up your /etc/raidtab
382	appropriately (see man 5 raidtab).
384	Linear volume sets, i.e. linear raid, as well as stripe sets, i.e. raid level
385	0, have been tested and work fine (though see section "Limitations when using
386	the MD driver with NTFS volumes" especially if you want to use linear raid).
387	Even though untested, there is no reason why mirrors, i.e. raid level 1, and
388	stripes with parity, i.e. raid level 5, should not work, too.
390	You have to use the "persistent-superblock 0" option for each raid-disk in the
391	NTFS volume/stripe you are configuring in /etc/raidtab as the persistent
392	superblock used by the MD driver would damage the NTFS volume.
394	Windows by default uses a stripe chunk size of 64k, so you probably want the
395	"chunk-size 64k" option for each raid-disk, too.
397	For example, if you have a stripe set consisting of two partitions /dev/hda5
398	and /dev/hdb1 your /etc/raidtab would look like this:
400	raiddev /dev/md0
401		raid-level	0
402		nr-raid-disks	2
403		nr-spare-disks	0
404		persistent-superblock	0
405		chunk-size	64k
406		device		/dev/hda5
407		raid-disk	0
408		device		/dev/hdb1
409		raid-disk	1
411	For linear raid, just change the raid-level above to "raid-level linear", for
412	mirrors, change it to "raid-level 1", and for stripe sets with parity, change
413	it to "raid-level 5".
415	Note for stripe sets with parity you will also need to tell the MD driver
416	which parity algorithm to use by specifying the option "parity-algorithm
417	which", where you need to replace "which" with the name of the algorithm to
418	use (see man 5 raidtab for available algorithms) and you will have to try the
419	different available algorithms until you find one that works.  Make sure you
420	are working read-only when playing with this as you may damage your data
421	otherwise.  If you find which algorithm works please let us know (email the
422	linux-ntfs developers list linux-ntfs-dev@lists.sourceforge.net or drop in on
423	IRC in channel #ntfs on the irc.freenode.net network) so we can update this
424	documentation.
426	Once the raidtab is setup, run for example raid0run -a to start all devices or
427	raid0run /dev/md0 to start a particular md device, in this case /dev/md0.
429	Then just use the mount command as usual to mount the ntfs volume using for
430	example:	mount -t ntfs -o ro /dev/md0 /mnt/myntfsvolume
432	It is advisable to do the mount read-only to see if the md volume has been
433	setup correctly to avoid the possibility of causing damage to the data on the
434	ntfs volume.
437	Limitations when using the Software RAID / MD driver
438	-----------------------------------------------------
440	Using the md driver will not work properly if any of your NTFS partitions have
441	an odd number of sectors.  This is especially important for linear raid as all
442	data after the first partition with an odd number of sectors will be offset by
443	one or more sectors so if you mount such a partition with write support you
444	will cause massive damage to the data on the volume which will only become
445	apparent when you try to use the volume again under Windows.
447	So when using linear raid, make sure that all your partitions have an even
448	number of sectors BEFORE attempting to use it.  You have been warned!
450	Even better is to simply use the Device-Mapper for linear raid and then you do
451	not have this problem with odd numbers of sectors.
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.