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diff --git a/Documentation/filesystems/ntfs.rst b/Documentation/filesystems/ntfs.rst new file mode 100644 index 000000000..5bb093a26 --- /dev/null +++ b/Documentation/filesystems/ntfs.rst @@ -0,0 +1,466 @@ +.. 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. |