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Changelog is in git history, no need to have a copy in the documentation. Signed-off-by: Anton Altaparmakov <anton@tuxera.com>
451 lines
20 KiB
Text
451 lines
20 KiB
Text
The Linux NTFS filesystem driver
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================================
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Table of contents
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=================
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- Overview
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- Web site
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- Features
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- Supported mount options
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- Known bugs and (mis-)features
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- Using NTFS volume and stripe sets
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- The Device-Mapper driver
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- The Software RAID / MD driver
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- Limitations when using the MD driver
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Overview
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========
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Linux-NTFS comes with a number of user-space programs known as ntfsprogs.
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These include mkntfs, a full-featured ntfs filesystem format utility,
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ntfsundelete used for recovering files that were unintentionally deleted
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from an NTFS volume and ntfsresize which is used to resize an NTFS partition.
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See the web site for more information.
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To mount an NTFS 1.2/3.x (Windows NT4/2000/XP/2003) volume, use the file
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system type 'ntfs'. The driver currently supports read-only mode (with no
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fault-tolerance, encryption or journalling) and very limited, but safe, write
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support.
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For fault tolerance and raid support (i.e. volume and stripe sets), you can
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use the kernel's Software RAID / MD driver. See section "Using Software RAID
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with NTFS" for details.
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Web site
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========
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There is plenty of additional information on the linux-ntfs web site
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at http://www.linux-ntfs.org/
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The web site has a lot of additional information, such as a comprehensive
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FAQ, documentation on the NTFS on-disk format, information on the Linux-NTFS
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userspace utilities, etc.
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Features
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========
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- This is a complete rewrite of the NTFS driver that used to be in the 2.4 and
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earlier kernels. This new driver implements NTFS read support and is
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functionally equivalent to the old ntfs driver and it also implements limited
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write support. The biggest limitation at present is that files/directories
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cannot be created or deleted. See below for the list of write features that
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are so far supported. Another limitation is that writing to compressed files
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is not implemented at all. Also, neither read nor write access to encrypted
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files is so far implemented.
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- The new driver has full support for sparse files on NTFS 3.x volumes which
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the old driver isn't happy with.
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- The new driver supports execution of binaries due to mmap() now being
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supported.
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- The new driver supports loopback mounting of files on NTFS which is used by
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some Linux distributions to enable the user to run Linux from an NTFS
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partition by creating a large file while in Windows and then loopback
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mounting the file while in Linux and creating a Linux filesystem on it that
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is used to install Linux on it.
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- A comparison of the two drivers using:
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time find . -type f -exec md5sum "{}" \;
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run three times in sequence with each driver (after a reboot) on a 1.4GiB
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NTFS partition, showed the new driver to be 20% faster in total time elapsed
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(from 9:43 minutes on average down to 7:53). The time spent in user space
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was unchanged but the time spent in the kernel was decreased by a factor of
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2.5 (from 85 CPU seconds down to 33).
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- The driver does not support short file names in general. For backwards
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compatibility, we implement access to files using their short file names if
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they exist. The driver will not create short file names however, and a
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rename will discard any existing short file name.
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- The new driver supports exporting of mounted NTFS volumes via NFS.
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- The new driver supports async io (aio).
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- The new driver supports fsync(2), fdatasync(2), and msync(2).
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- The new driver supports readv(2) and writev(2).
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- The new driver supports access time updates (including mtime and ctime).
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- The new driver supports truncate(2) and open(2) with O_TRUNC. But at present
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only very limited support for highly fragmented files, i.e. ones which have
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their data attribute split across multiple extents, is included. Another
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limitation is that at present truncate(2) will never create sparse files,
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since to mark a file sparse we need to modify the directory entry for the
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file and we do not implement directory modifications yet.
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- The new driver supports write(2) which can both overwrite existing data and
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extend the file size so that you can write beyond the existing data. Also,
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writing into sparse regions is supported and the holes are filled in with
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clusters. But at present only limited support for highly fragmented files,
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i.e. ones which have their data attribute split across multiple extents, is
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included. Another limitation is that write(2) will never create sparse
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files, since to mark a file sparse we need to modify the directory entry for
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the file and we do not implement directory modifications yet.
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Supported mount options
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=======================
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In addition to the generic mount options described by the manual page for the
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mount command (man 8 mount, also see man 5 fstab), the NTFS driver supports the
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following mount options:
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iocharset=name Deprecated option. Still supported but please use
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nls=name in the future. See description for nls=name.
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nls=name Character set to use when returning file names.
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Unlike VFAT, NTFS suppresses names that contain
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unconvertible characters. Note that most character
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sets contain insufficient characters to represent all
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possible Unicode characters that can exist on NTFS.
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To be sure you are not missing any files, you are
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advised to use nls=utf8 which is capable of
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representing all Unicode characters.
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utf8=<bool> Option no longer supported. Currently mapped to
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nls=utf8 but please use nls=utf8 in the future and
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make sure utf8 is compiled either as module or into
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the kernel. See description for nls=name.
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uid=
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gid=
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umask= Provide default owner, group, and access mode mask.
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These options work as documented in mount(8). By
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default, the files/directories are owned by root and
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he/she has read and write permissions, as well as
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browse permission for directories. No one else has any
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access permissions. I.e. the mode on all files is by
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default rw------- and for directories rwx------, a
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consequence of the default fmask=0177 and dmask=0077.
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Using a umask of zero will grant all permissions to
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everyone, i.e. all files and directories will have mode
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rwxrwxrwx.
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fmask=
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dmask= Instead of specifying umask which applies both to
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files and directories, fmask applies only to files and
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dmask only to directories.
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sloppy=<BOOL> If sloppy is specified, ignore unknown mount options.
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Otherwise the default behaviour is to abort mount if
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any unknown options are found.
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show_sys_files=<BOOL> If show_sys_files is specified, show the system files
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in directory listings. Otherwise the default behaviour
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is to hide the system files.
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Note that even when show_sys_files is specified, "$MFT"
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will not be visible due to bugs/mis-features in glibc.
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Further, note that irrespective of show_sys_files, all
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files are accessible by name, i.e. you can always do
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"ls -l \$UpCase" for example to specifically show the
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system file containing the Unicode upcase table.
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case_sensitive=<BOOL> If case_sensitive is specified, treat all file names as
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case sensitive and create file names in the POSIX
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namespace. Otherwise the default behaviour is to treat
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file names as case insensitive and to create file names
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in the WIN32/LONG name space. Note, the Linux NTFS
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driver will never create short file names and will
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remove them on rename/delete of the corresponding long
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file name.
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Note that files remain accessible via their short file
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name, if it exists. If case_sensitive, you will need
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to provide the correct case of the short file name.
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disable_sparse=<BOOL> If disable_sparse is specified, creation of sparse
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regions, i.e. holes, inside files is disabled for the
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volume (for the duration of this mount only). By
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default, creation of sparse regions is enabled, which
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is consistent with the behaviour of traditional Unix
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filesystems.
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errors=opt What to do when critical filesystem errors are found.
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Following values can be used for "opt":
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continue: DEFAULT, try to clean-up as much as
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possible, e.g. marking a corrupt inode as
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bad so it is no longer accessed, and then
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continue.
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recover: At present only supported is recovery of
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the boot sector from the backup copy.
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If read-only mount, the recovery is done
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in memory only and not written to disk.
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Note that the options are additive, i.e. specifying:
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errors=continue,errors=recover
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means the driver will attempt to recover and if that
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fails it will clean-up as much as possible and
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continue.
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mft_zone_multiplier= Set the MFT zone multiplier for the volume (this
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setting is not persistent across mounts and can be
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changed from mount to mount but cannot be changed on
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remount). Values of 1 to 4 are allowed, 1 being the
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default. The MFT zone multiplier determines how much
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space is reserved for the MFT on the volume. If all
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other space is used up, then the MFT zone will be
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shrunk dynamically, so this has no impact on the
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amount of free space. However, it can have an impact
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on performance by affecting fragmentation of the MFT.
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In general use the default. If you have a lot of small
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files then use a higher value. The values have the
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following meaning:
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Value MFT zone size (% of volume size)
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1 12.5%
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2 25%
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3 37.5%
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4 50%
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Note this option is irrelevant for read-only mounts.
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Known bugs and (mis-)features
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=============================
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- The link count on each directory inode entry is set to 1, due to Linux not
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supporting directory hard links. This may well confuse some user space
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applications, since the directory names will have the same inode numbers.
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This also speeds up ntfs_read_inode() immensely. And we haven't found any
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problems with this approach so far. If you find a problem with this, please
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let us know.
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Please send bug reports/comments/feedback/abuse to the Linux-NTFS development
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list at sourceforge: linux-ntfs-dev@lists.sourceforge.net
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Using NTFS volume and stripe sets
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=================================
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For support of volume and stripe sets, you can either use the kernel's
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Device-Mapper driver or the kernel's Software RAID / MD driver. The former is
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the recommended one to use for linear raid. But the latter is required for
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raid level 5. For striping and mirroring, either driver should work fine.
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The Device-Mapper driver
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------------------------
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You will need to create a table of the components of the volume/stripe set and
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how they fit together and load this into the kernel using the dmsetup utility
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(see man 8 dmsetup).
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Linear volume sets, i.e. linear raid, has been tested and works fine. Even
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though untested, there is no reason why stripe sets, i.e. raid level 0, and
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mirrors, i.e. raid level 1 should not work, too. Stripes with parity, i.e.
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raid level 5, unfortunately cannot work yet because the current version of the
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Device-Mapper driver does not support raid level 5. You may be able to use the
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Software RAID / MD driver for raid level 5, see the next section for details.
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To create the table describing your volume you will need to know each of its
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components and their sizes in sectors, i.e. multiples of 512-byte blocks.
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For NT4 fault tolerant volumes you can obtain the sizes using fdisk. So for
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example if one of your partitions is /dev/hda2 you would do:
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$ fdisk -ul /dev/hda
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Disk /dev/hda: 81.9 GB, 81964302336 bytes
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255 heads, 63 sectors/track, 9964 cylinders, total 160086528 sectors
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Units = sectors of 1 * 512 = 512 bytes
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Device Boot Start End Blocks Id System
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/dev/hda1 * 63 4209029 2104483+ 83 Linux
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/dev/hda2 4209030 37768814 16779892+ 86 NTFS
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/dev/hda3 37768815 46170809 4200997+ 83 Linux
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And you would know that /dev/hda2 has a size of 37768814 - 4209030 + 1 =
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33559785 sectors.
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For Win2k and later dynamic disks, you can for example use the ldminfo utility
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which is part of the Linux LDM tools (the latest version at the time of
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writing is linux-ldm-0.0.8.tar.bz2). You can download it from:
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http://www.linux-ntfs.org/
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Simply extract the downloaded archive (tar xvjf linux-ldm-0.0.8.tar.bz2), go
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into it (cd linux-ldm-0.0.8) and change to the test directory (cd test). You
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will find the precompiled (i386) ldminfo utility there. NOTE: You will not be
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able to compile this yourself easily so use the binary version!
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Then you would use ldminfo in dump mode to obtain the necessary information:
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$ ./ldminfo --dump /dev/hda
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This would dump the LDM database found on /dev/hda which describes all of your
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dynamic disks and all the volumes on them. At the bottom you will see the
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VOLUME DEFINITIONS section which is all you really need. You may need to look
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further above to determine which of the disks in the volume definitions is
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which device in Linux. Hint: Run ldminfo on each of your dynamic disks and
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look at the Disk Id close to the top of the output for each (the PRIVATE HEADER
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section). You can then find these Disk Ids in the VBLK DATABASE section in the
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<Disk> components where you will get the LDM Name for the disk that is found in
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the VOLUME DEFINITIONS section.
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Note you will also need to enable the LDM driver in the Linux kernel. If your
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distribution did not enable it, you will need to recompile the kernel with it
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enabled. This will create the LDM partitions on each device at boot time. You
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would then use those devices (for /dev/hda they would be /dev/hda1, 2, 3, etc)
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in the Device-Mapper table.
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You can also bypass using the LDM driver by using the main device (e.g.
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/dev/hda) and then using the offsets of the LDM partitions into this device as
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the "Start sector of device" when creating the table. Once again ldminfo would
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give you the correct information to do this.
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Assuming you know all your devices and their sizes things are easy.
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For a linear raid the table would look like this (note all values are in
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512-byte sectors):
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--- cut here ---
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# Offset into Size of this Raid type Device Start sector
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# volume device of device
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0 1028161 linear /dev/hda1 0
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1028161 3903762 linear /dev/hdb2 0
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4931923 2103211 linear /dev/hdc1 0
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--- cut here ---
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For a striped volume, i.e. raid level 0, you will need to know the chunk size
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you used when creating the volume. Windows uses 64kiB as the default, so it
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will probably be this unless you changes the defaults when creating the array.
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For a raid level 0 the table would look like this (note all values are in
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512-byte sectors):
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--- cut here ---
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# Offset Size Raid Number Chunk 1st Start 2nd Start
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# into of the type of size Device in Device in
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# volume volume stripes device device
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0 2056320 striped 2 128 /dev/hda1 0 /dev/hdb1 0
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--- cut here ---
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If there are more than two devices, just add each of them to the end of the
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line.
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Finally, for a mirrored volume, i.e. raid level 1, the table would look like
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this (note all values are in 512-byte sectors):
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--- cut here ---
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# Ofs Size Raid Log Number Region Should Number Source Start Target Start
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# in of the type type of log size sync? of Device in Device in
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# vol volume params mirrors Device Device
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0 2056320 mirror core 2 16 nosync 2 /dev/hda1 0 /dev/hdb1 0
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--- cut here ---
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If you are mirroring to multiple devices you can specify further targets at the
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end of the line.
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Note the "Should sync?" parameter "nosync" means that the two mirrors are
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already in sync which will be the case on a clean shutdown of Windows. If the
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mirrors are not clean, you can specify the "sync" option instead of "nosync"
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and the Device-Mapper driver will then copy the entirety of the "Source Device"
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to the "Target Device" or if you specified multiple target devices to all of
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them.
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Once you have your table, save it in a file somewhere (e.g. /etc/ntfsvolume1),
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and hand it over to dmsetup to work with, like so:
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$ dmsetup create myvolume1 /etc/ntfsvolume1
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You can obviously replace "myvolume1" with whatever name you like.
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If it all worked, you will now have the device /dev/device-mapper/myvolume1
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which you can then just use as an argument to the mount command as usual to
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mount the ntfs volume. For example:
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$ mount -t ntfs -o ro /dev/device-mapper/myvolume1 /mnt/myvol1
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(You need to create the directory /mnt/myvol1 first and of course you can use
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anything you like instead of /mnt/myvol1 as long as it is an existing
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directory.)
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It is advisable to do the mount read-only to see if the volume has been setup
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correctly to avoid the possibility of causing damage to the data on the ntfs
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volume.
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The Software RAID / MD driver
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-----------------------------
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An alternative to using the Device-Mapper driver is to use the kernel's
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Software RAID / MD driver. For which you need to set up your /etc/raidtab
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appropriately (see man 5 raidtab).
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Linear volume sets, i.e. linear raid, as well as stripe sets, i.e. raid level
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0, have been tested and work fine (though see section "Limitations when using
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the MD driver with NTFS volumes" especially if you want to use linear raid).
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Even though untested, there is no reason why mirrors, i.e. raid level 1, and
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stripes with parity, i.e. raid level 5, should not work, too.
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You have to use the "persistent-superblock 0" option for each raid-disk in the
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NTFS volume/stripe you are configuring in /etc/raidtab as the persistent
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superblock used by the MD driver would damage the NTFS volume.
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Windows by default uses a stripe chunk size of 64k, so you probably want the
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"chunk-size 64k" option for each raid-disk, too.
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For example, if you have a stripe set consisting of two partitions /dev/hda5
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and /dev/hdb1 your /etc/raidtab would look like this:
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raiddev /dev/md0
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raid-level 0
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nr-raid-disks 2
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nr-spare-disks 0
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persistent-superblock 0
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chunk-size 64k
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device /dev/hda5
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raid-disk 0
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device /dev/hdb1
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raid-disk 1
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For linear raid, just change the raid-level above to "raid-level linear", for
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mirrors, change it to "raid-level 1", and for stripe sets with parity, change
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it to "raid-level 5".
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Note for stripe sets with parity you will also need to tell the MD driver
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which parity algorithm to use by specifying the option "parity-algorithm
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which", where you need to replace "which" with the name of the algorithm to
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use (see man 5 raidtab for available algorithms) and you will have to try the
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different available algorithms until you find one that works. Make sure you
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are working read-only when playing with this as you may damage your data
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otherwise. If you find which algorithm works please let us know (email the
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linux-ntfs developers list linux-ntfs-dev@lists.sourceforge.net or drop in on
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IRC in channel #ntfs on the irc.freenode.net network) so we can update this
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documentation.
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Once the raidtab is setup, run for example raid0run -a to start all devices or
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raid0run /dev/md0 to start a particular md device, in this case /dev/md0.
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Then just use the mount command as usual to mount the ntfs volume using for
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example: mount -t ntfs -o ro /dev/md0 /mnt/myntfsvolume
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It is advisable to do the mount read-only to see if the md volume has been
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setup correctly to avoid the possibility of causing damage to the data on the
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ntfs volume.
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Limitations when using the Software RAID / MD driver
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-----------------------------------------------------
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Using the md driver will not work properly if any of your NTFS partitions have
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an odd number of sectors. This is especially important for linear raid as all
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data after the first partition with an odd number of sectors will be offset by
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one or more sectors so if you mount such a partition with write support you
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will cause massive damage to the data on the volume which will only become
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apparent when you try to use the volume again under Windows.
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So when using linear raid, make sure that all your partitions have an even
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number of sectors BEFORE attempting to use it. You have been warned!
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Even better is to simply use the Device-Mapper for linear raid and then you do
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not have this problem with odd numbers of sectors.
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