1 .\" Copyright (c) 2007 The DragonFly Project. All rights reserved.
3 .\" This code is derived from software contributed to The DragonFly Project
4 .\" by Matthew Dillon <dillon@backplane.com>
6 .\" Redistribution and use in source and binary forms, with or without
7 .\" modification, are permitted provided that the following conditions
10 .\" 1. Redistributions of source code must retain the above copyright
11 .\" notice, this list of conditions and the following disclaimer.
12 .\" 2. Redistributions in binary form must reproduce the above copyright
13 .\" notice, this list of conditions and the following disclaimer in
14 .\" the documentation and/or other materials provided with the
16 .\" 3. Neither the name of The DragonFly Project nor the names of its
17 .\" contributors may be used to endorse or promote products derived
18 .\" from this software without specific, prior written permission.
20 .\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
21 .\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
22 .\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
23 .\" FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
24 .\" COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
25 .\" INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
26 .\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
27 .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
28 .\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
29 .\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
30 .\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 .\" $DragonFly: src/sbin/hammer/hammer.8,v 1.58 2008/11/13 02:04:27 dillon Exp $
40 .Nd HAMMER file system utility
49 .\" .Op Fl s Ar linkpath
53 .Op Fl C Ar cachesize Ns Op Ns Cm \&: Ns Ar readahead
58 This manual page documents the
60 utility which provides miscellaneous functions related to managing a
63 For a general introduction to the
65 file system, its features, and
66 examples on how to set up and maintain one, see
69 The options are as follows:
70 .Bl -tag -width indent
74 Tell the mirror commands to use a 2-way protocol, which allows
75 automatic negotiation of transaction id ranges.
76 This option is automatically enabled by the
80 Specify a bandwidth limit in bytes per second for mirroring streams.
81 This option is typically used to prevent batch mirroring operations from
82 loading down the machine.
83 The bandwidth may be suffixed with
87 to specify values in kilobytes, megabytes, and gigabytes per second.
88 If no suffix is specified, bytes per second is assumed.
90 Unfortunately this is only applicable to the pre-compression bandwidth
91 when compression is used, so a better solution would probably be to
98 When pruning, rebalancing or reblocking you can tell the utility
99 to start at the object id stored in the specified file.
100 If the file does not exist
102 will start at the beginning.
106 specific period of time and is unable to complete the operation it will
107 write out the current object id so the next run can pick up where it left off.
110 runs to completion it will delete
113 Specify the volumes making up a
117 is a colon-separated list of devices, each specifying a
121 When maintaining a streaming mirroring this option specifies the
122 minimum delay after a batch ends before the next batch is allowed
124 The default is five seconds.
131 specification for the source and/or destination.
133 Decrease verboseness.
134 May be specified multiple times.
136 Specify recursion for those commands which support it.
138 When pruning, rebalancing or reblocking you can tell the utility to stop
139 after a certain period of time.
140 This option is used along with the
142 option to prune, rebalance or reblock incrementally.
144 Increase verboseness.
145 May be specified multiple times.
147 Force "yes" for any interactive question.
151 will not attempt to break-up large initial bulk transfers into smaller
153 This can save time but if the link is lost in the middle of the
154 initial bulk transfer you will have to start over from scratch.
155 This option is not recommended.
156 For more information see the
159 .It Fl C Ar cachesize Ns Op Ns Cm \&: Ns Ar readahead
160 Set the memory cache size for any raw
167 for megabytes is allowed,
168 else the cache size is specified in bytes.
170 The read-behind/read-ahead defaults to 4
174 This option is typically only used with diagnostic commands
175 as kernel-supported commands will use the kernel's buffer cache.
176 .It Fl S Ar splitsize
177 Specify the bulk splitup size in bytes for mirroring streams.
182 will do an initial run-through of the data to calculate good
183 transaction ids to cut up the bulk transfers, creating
184 restart points in case the stream is interrupted.
185 If we don't do this and the stream is interrupted it might
186 have to start all over again.
187 The default is a splitsize of 4G.
189 At the moment the run-through is disk-bandwidth-heavy but some
190 future version will limit the run-through to just the B-Tree
191 records and not the record data.
193 The splitsize may be suffixed with
197 to specify values in kilobytes, megabytes, or gigabytes.
198 If no suffix is specified, bytes is assumed.
200 When mirroring very large filesystems the minimum recommended
202 A small split size may wind up generating a great deal of overhead
203 but very little actual incremental data and is not recommended.
205 Enable compression for any remote ssh specifications.
208 option has already been reserved for other purposes so we had to use
210 This option is typically used with the mirroring directives.
212 Force "yes" for any interactive question.
215 The commands are as follows:
216 .Bl -tag -width indent
217 .\" ==== synctid ====
218 .It Cm synctid Ar filesystem Op Cm quick
219 Generates a guaranteed, formal 64 bit transaction id representing the
220 current state of the specified
223 The file system will be synced to the media.
227 keyword is specified the file system will be soft-synced, meaning that a
228 crash might still undo the state of the file system as of the transaction
229 id returned but any new modifications will occur after the returned
230 transaction id as expected.
232 This operation does not create a snapshot.
233 It is meant to be used
234 to track temporary fine-grained changes to a subset of files and
235 will only remain valid for
237 snapshot access purposes for the
239 period configured for the PFS.
240 If you desire a real snapshot then the
242 directive may be what you are looking for.
244 .It Cm bstats Op Ar interval
247 B-Tree statistics until interrupted.
250 seconds between each display.
251 The default interval is one second.
252 .\" ==== iostats ====
253 .It Cm iostats Op Ar interval
257 statistics until interrupted.
260 seconds between each display.
261 The default interval is one second.
262 .\" ==== history ====
263 .It Cm history Ar path ...
264 Show the modification history for
266 file's inode and data.
267 .\" ==== blockmap ====
269 Dump the blockmap for the file system.
272 blockmap is two-layer
273 blockmap representing the maximum possible file system size of 1 Exabyte.
274 Needless to say the second layer is only present for blocks which exist.
276 blockmap represents 8-Megabyte blocks, called big-blocks.
277 Each big-block has an append
278 point, a free byte count, and a typed zone id which allows content to be
279 reverse engineered to some degree.
283 allocations are essentially appended to a selected big-block using
284 the append offset and deducted from the free byte count.
285 When space is freed the free byte count is adjusted but
287 does not track holes in big-blocks for reallocation.
288 A big-block must be completely freed, either
289 through normal file system operations or through reblocking, before
292 Data blocks can be shared by deducting the space used from the free byte
293 count for each shared references, though
295 does not yet make use of this feature.
296 This means the free byte count can legally go negative.
298 This command needs the
301 .\" ==== checkmap ====
303 Check the blockmap allocation count.
305 will scan the B-Tree, collect allocation information, and
306 construct a blockmap in-memory. It will then check that blockmap
307 against the on-disk blockmap.
309 .It Cm show Op Ar lo Ns Cm \&: Ns Ar objid
311 By default this command will validate all B-Tree
312 linkages and CRCs, including data CRCs, and will report the most verbose
313 information it can dig up.
314 Any errors will show up with a
316 in column 1 along with various
319 If you specify a localization field or a localization:obj_id field,
320 .Ar lo Ns Cm \&: Ns Ar objid ,
322 search for the key printing nodes as it recurses down, and then
323 will iterate forwards.
324 These fields are specified in HEX.
325 Note that the pfsid is the top 16 bits of the 32 bit localization
326 field so PFS #1 would be 00010000.
330 the command will report less information about the inode contents.
334 the command will not report the content of the inode or other typed
339 the command will not report volume header information, big-block fill
340 ratios, mirror transaction ids, or report or check data CRCs.
341 B-Tree CRCs and linkages are still checked.
343 This command needs the
346 .\" ==== show-undo ====
352 This command needs the
356 .\" Dump the B-Tree, record, large-data, and small-data blockmaps, showing
357 .\" physical block assignments and free space percentages.
358 .\" ==== recover ====
359 .It Cm recover Ar targetdir
360 This is a low level command which operates on the filesystem image and
361 attempts to locate and recover files from a corrupted filesystem. The
362 entire image is scanned linearly looking for B-Tree nodes. Any node
363 found which passes its crc test is scanned for file, inode, and directory
364 fragments and the target directory is populated with the resulting data.
365 files and directories in the target directory are initially named after
366 the object id and are renamed as fragmentory information is processed.
368 This command keeps track of filename/objid translations and may eat a
369 considerably amount of memory while operating.
371 This command is literally the last line of defense when it comes to
372 recovering data from a dead filesystem.
373 .\" ==== namekey1 ====
374 .It Cm namekey1 Ar filename
377 64 bit directory hash for the specified file name, using
378 the original directory hash algorithm in version 1 of the file system.
379 The low 32 bits are used as an iterator for hash collisions and will be
381 .\" ==== namekey2 ====
382 .It Cm namekey2 Ar filename
385 64 bit directory hash for the specified file name, using
386 the new directory hash algorithm in version 2 of the file system.
387 The low 32 bits are still used as an iterator but will start out containing
388 part of the hash key.
389 .\" ==== namekey32 ====
390 .It Cm namekey32 Ar filename
391 Generate the top 32 bits of a
393 64 bit directory hash for the specified file name.
396 Shows extended information about all the mounted
399 The information is divided into sections:
400 .Bl -tag -width indent
401 .It Volume identification
402 General information, like the label of the
404 filesystem, the number of volumes it contains, the FSID, and the
407 .It Big block information
408 Big block statistics, such as total, used, reserved and free big blocks.
409 .It Space information
410 Information about space used on the filesystem.
411 Currently total size, used, reserved and free space are displayed.
413 Basic information about the PFSs currently present on a
418 is the ID of the PFS, with 0 being the root PFS.
420 is the current snapshot count on the PFS.
422 displays the mount point of the PFS is currently mounted on (if any).
424 .\" ==== cleanup ====
425 .It Cm cleanup Op Ar filesystem ...
426 This is a meta-command which executes snapshot, prune, rebalance and reblock
427 commands on the specified
432 is specified this command will clean-up all
434 file systems in use, including PFS's.
435 To do this it will scan all
439 mounts, extract PFS id's, and clean-up each PFS found.
441 This command will access a snapshots
442 directory and a configuration file for each
444 creating them if necessary.
445 .Bl -tag -width indent
446 .It Nm HAMMER No version 2-
447 The configuration file is
449 in the snapshots directory which defaults to
450 .Pa <pfs>/snapshots .
451 .It Nm HAMMER No version 3+
452 The configuration file is saved in file system meta-data, see
455 The snapshots directory defaults to
456 .Pa /var/hammer/<pfs>
457 .Pa ( /var/hammer/root
461 The format of the configuration file is:
462 .Bd -literal -offset indent
463 snapshots <period> <retention-time> [any]
464 prune <period> <max-runtime>
465 rebalance <period> <max-runtime>
466 reblock <period> <max-runtime>
467 recopy <period> <max-runtime>
471 .Bd -literal -offset indent
472 snapshots 1d 60d # 0d 0d for PFS /tmp, /var/tmp, /usr/obj
479 Time is given with a suffix of
485 meaning day, hour, minute and second.
489 directive has a period of 0 and a retention time of 0
490 then snapshot generation is disabled, removal of old snapshots are
491 disabled, and prunes will use
492 .Cm prune-everything .
495 directive has a period of 0 but a non-zero retention time
496 then this command will not create any new snapshots but will remove old
497 snapshots it finds based on the retention time.
499 By default only snapshots in the form
500 .Ql snap- Ns Ar yyyymmdd Ns Op - Ns Ar HHMM
504 directive is specified as a third argument on the
506 config line then any softlink of the form
507 .Ql *- Ns Ar yyyymmdd Ns Op - Ns Ar HHMM
509 .Ql *. Ns Ar yyyymmdd Ns Op - Ns Ar HHMM
512 A prune max-runtime of 0 means unlimited.
514 If period hasn't passed since the previous
517 For example a day has passed when midnight is passed (localtime).
525 The default configuration file will create a daily snapshot, do a daily
526 pruning, rebalancing and reblocking run and a monthly recopy run.
527 Reblocking is defragmentation with a level of 95%,
528 and recopy is full defragmentation.
530 By default prune and rebalance operations are time limited to 5 minutes,
531 reblock operations to a bit over 5 minutes,
532 and recopy operations to a bit over 10 minutes.
533 Reblocking and recopy runs are each broken down into four separate functions:
534 btree, inodes, dirs and data.
535 Each function is time limited to the time given in the configuration file,
536 but the btree, inodes and dirs functions usually does not take very long time,
537 full defragmentation is always used for these three functions.
538 Also note that this directive will by default disable snapshots on
545 The defaults may be adjusted by modifying the configuration file.
546 The pruning and reblocking commands automatically maintain a cyclefile
547 for incremental operation.
548 If you interrupt (^C) the program the cyclefile will be updated,
550 may continue to run in the background for a few seconds until the
552 ioctl detects the interrupt.
555 PFS option can be set to use another location for the snapshots directory.
557 Work on this command is still in progress.
559 An ability to remove snapshots dynamically as the
560 file system becomes full.
562 .It Cm config Op Ar filesystem Op Ar configfile
565 Show or change configuration for
567 If zero or one arguments are specified this function dumps the current
568 configuration file to stdout.
569 Zero arguments specifies the PFS containing the current directory.
570 This configuration file is stored in file system meta-data.
571 If two arguments are specified this function installs a new config file.
575 versions less than 3 the configuration file is by default stored in
576 .Pa <pfs>/snapshots/config ,
577 but in all later versions the configuration file is stored in file system
579 .\" ==== viconfig ====
580 .It Cm viconfig Op Ar filesystem
583 Edit the configuration file and reinstall into file system meta-data when done.
584 Zero arguments specifies the PFS containing the current directory.
585 .\" ==== volume-add ====
586 .It Cm volume-add Ar device Ar filesystem
587 This command will format
589 and add all of its space to
593 All existing data contained on
595 will be destroyed by this operation!
600 file system, formatting will be denied.
601 You can overcome this sanity check
604 to erase the beginning sectors of the device.
605 Also remember that you have to specify
607 together with any other device that make up the file system,
612 .\" ==== volume-del ====
613 .It Cm volume-del Ar device Ar filesystem
614 This command will remove volume
619 Remember that you have to remove
621 from the colon-separated list in
625 .\" ==== snapshot ====
626 .It Cm snapshot Oo Ar filesystem Oc Ar snapshot-dir
627 .It Cm snapshot Ar filesystem Ar snapshot-dir Op Ar note
628 Takes a snapshot of the file system either explicitly given by
630 or implicitly derived from the
632 argument and creates a symlink in the directory provided by
634 pointing to the snapshot.
637 is not a directory, it is assumed to be a format string passed to
639 with the current time as parameter.
642 refers to an existing directory, a default format string of
644 is assumed and used as name for the newly created symlink.
646 Snapshot is a per PFS operation, so a
648 file system and each PFS in it have to be snapshot separately.
650 Example, assuming that
658 are file systems on their own, the following invocations:
659 .Bd -literal -offset indent
660 hammer snapshot /mysnapshots
662 hammer snapshot /mysnapshots/%Y-%m-%d
664 hammer snapshot /obj /mysnapshots/obj-%Y-%m-%d
666 hammer snapshot /usr /my/snaps/usr "note"
669 Would create symlinks similar to:
670 .Bd -literal -offset indent
671 /mysnapshots/snap-20080627-1210 -> /@@0x10d2cd05b7270d16
673 /mysnapshots/2008-06-27 -> /@@0x10d2cd05b7270d16
675 /mysnapshots/obj-2008-06-27 -> /obj@@0x10d2cd05b7270d16
677 /my/snaps/usr/snap-20080627-1210 -> /usr@@0x10d2cd05b7270d16
682 version 3+ file system the snapshot is also recorded in file system meta-data
683 along with the optional
689 .It Cm snap Ar path Op Ar note
692 Create a snapshot for the PFS containing
694 and create a snapshot softlink.
695 If the path specified is a
696 directory a standard snapshot softlink will be created in the directory.
697 The snapshot softlink points to the base of the mounted PFS.
698 .It Cm snaplo Ar path Op Ar note
701 Create a snapshot for the PFS containing
703 and create a snapshot softlink.
704 If the path specified is a
705 directory a standard snapshot softlink will be created in the directory.
706 The snapshot softlink points into the directory it is contained in.
707 .It Cm snapq Ar dir Op Ar note
710 Create a snapshot for the PFS containing the specified directory but do
711 not create a softlink.
712 Instead output a path which can be used to access
713 the directory via the snapshot.
715 An absolute or relative path may be specified.
716 The path will be used as-is as a prefix in the path output to stdout.
718 snap and snapshot directives the snapshot transaction id will be registered
719 in the file system meta-data.
720 .It Cm snaprm Ar path Ar ...
721 .It Cm snaprm Ar transid Ar ...
722 .It Cm snaprm Ar filesystem Ar transid Ar ...
725 Remove a snapshot given its softlink or transaction id.
726 If specifying a transaction id
727 the snapshot is removed from file system meta-data but you are responsible
728 for removing any related softlinks.
730 If a softlink path is specified the filesystem and transaction id
731 is derived from the contents of the softlink.
732 If just a transaction id is specified it is assumed to be a snapshot
733 in the HAMMER filesystem you are currently chdir'd into.
734 You can also specify the filesystem and transaction id explicitly.
735 .It Cm snapls Op Ar path ...
738 Dump the snapshot meta-data for PFSs containing each
740 listing all available snapshots and their notes.
741 If no arguments are specified snapshots for the PFS containing the
742 current directory are listed.
743 This is the definitive list of snapshots for the file system.
745 .It Cm prune Ar softlink-dir
746 Prune the file system based on previously created snapshot softlinks.
747 Pruning is the act of deleting file system history.
750 command will delete file system history such that
751 the file system state is retained for the given snapshots,
752 and all history after the latest snapshot.
753 By setting the per PFS parameter
755 history is guaranteed to be saved at least this time interval.
756 All other history is deleted.
758 The target directory is expected to contain softlinks pointing to
759 snapshots of the file systems you wish to retain.
760 The directory is scanned non-recursively and the mount points and
761 transaction ids stored in the softlinks are extracted and sorted.
762 The file system is then explicitly pruned according to what is found.
763 Cleaning out portions of the file system is as simple as removing a
764 snapshot softlink and then running the
768 As a safety measure pruning only occurs if one or more softlinks are found
771 snapshot id extension.
772 Currently the scanned softlink directory must contain softlinks pointing
776 The softlinks may specify absolute or relative paths.
777 Softlinks must use 20-character
779 transaction ids, as might be returned from
780 .Nm Cm synctid Ar filesystem .
782 Pruning is a per PFS operation, so a
784 file system and each PFS in it have to be pruned separately.
786 Note that pruning a file system may not immediately free-up space,
787 though typically some space will be freed if a large number of records are
789 The file system must be reblocked to completely recover all available space.
791 Example, lets say your that you didn't set
793 and snapshot directory contains the following links:
794 .Bd -literal -offset indent
795 lrwxr-xr-x 1 root wheel 29 May 31 17:57 snap1 ->
796 /usr/obj/@@0x10d2cd05b7270d16
798 lrwxr-xr-x 1 root wheel 29 May 31 17:58 snap2 ->
799 /usr/obj/@@0x10d2cd13f3fde98f
801 lrwxr-xr-x 1 root wheel 29 May 31 17:59 snap3 ->
802 /usr/obj/@@0x10d2cd222adee364
805 If you were to run the
807 command on this directory, then the
810 mount will be pruned to retain the above three snapshots.
811 In addition, history for modifications made to the file system older than
812 the oldest snapshot will be destroyed and history for potentially fine-grained
813 modifications made to the file system more recently than the most recent
814 snapshot will be retained.
816 If you then delete the
818 softlink and rerun the
821 history for modifications pertaining to that snapshot would be destroyed.
825 file system versions 3+ this command also scans the snapshots stored
826 in the file system meta-data and includes them in the prune.
827 .\" ==== prune-everything ====
828 .It Cm prune-everything Ar filesystem
829 This command will remove all historical records from the file system.
830 This directive is not normally used on a production system.
832 This command does not remove snapshot softlinks but will delete all
833 snapshots recorded in file system meta-data (for file system version 3+).
834 The user is responsible for deleting any softlinks.
836 Pruning is a per PFS operation, so a
838 file system and each PFS in it have to be pruned separately.
839 .\" ==== rebalance ====
840 .It Cm rebalance Ar filesystem Op Ar saturation_percentage
841 This command will rebalance the B-Tree, nodes with small number of
842 elements will be combined and element counts will be smoothed out
845 The saturation percentage is between 50% and 100%.
846 The default is 75% (the
848 suffix is not needed).
850 Rebalancing is a per PFS operation, so a
852 file system and each PFS in it have to be rebalanced separately.
853 .\" ==== reblock* ====
854 .It Cm reblock Ar filesystem Op Ar fill_percentage
855 .It Cm reblock-btree Ar filesystem Op Ar fill_percentage
856 .It Cm reblock-inodes Ar filesystem Op Ar fill_percentage
857 .It Cm reblock-dirs Ar filesystem Op Ar fill_percentage
858 .It Cm reblock-data Ar filesystem Op Ar fill_percentage
859 Attempt to defragment and free space for reuse by reblocking a live
862 Big-blocks cannot be reused by
864 until they are completely free.
865 This command also has the effect of reordering all elements, effectively
866 defragmenting the file system.
868 The default fill percentage is 100% and will cause the file system to be
869 completely defragmented.
870 All specified element types will be reallocated and rewritten.
871 If you wish to quickly free up space instead try specifying
872 a smaller fill percentage, such as 90% or 80% (the
874 suffix is not needed).
876 Since this command may rewrite the entire contents of the disk it is
877 best to do it incrementally from a
883 options to limit the run time.
884 The file system would thus be defragmented over long period of time.
886 It is recommended that separate invocations be used for each data type.
887 B-Tree nodes, inodes, and directories are typically the most important
888 elements needing defragmentation.
889 Data can be defragmented over a longer period of time.
891 Reblocking is a per PFS operation, so a
893 file system and each PFS in it have to be reblocked separately.
894 .\" ==== pfs-status ====
895 .It Cm pfs-status Ar dirpath ...
896 Retrieve the mirroring configuration parameters for the specified
898 file systems or pseudo-filesystems (PFS's).
899 .\" ==== pfs-master ====
900 .It Cm pfs-master Ar dirpath Op Ar options
901 Create a pseudo-filesystem (PFS) inside a
904 Up to 65535 such file systems can be created.
905 Each PFS uses an independent inode numbering space making it suitable
906 for use as a replication source or target.
910 directive creates a PFS that you can read, write, and use as a mirroring
913 It is recommended to use a
915 mount to access a PFS, for more information see
917 .\" ==== pfs-slave ====
918 .It Cm pfs-slave Ar dirpath Op Ar options
919 Create a pseudo-filesystem (PFS) inside a
922 Up to 65535 such file systems can be created.
923 Each PFS uses an independent inode numbering space making it suitable
924 for use as a replication source or target.
928 directive creates a PFS that you can use as a mirroring target.
929 You will not be able to access a slave PFS until you have completed the
930 first mirroring operation with it as the target (its root directory will
931 not exist until then).
933 Access to the pfs-slave via the special softlink, as described in the
938 dynamically modify the snapshot transaction id by returning a dynamic result
943 A PFS can only be truly destroyed with the
946 Removing the softlink will not destroy the underlying PFS.
948 It is recommended to use a
950 mount to access a PFS, for more information see
952 .\" ==== pfs-update ====
953 .It Cm pfs-update Ar dirpath Op Ar options
954 Update the configuration parameters for an existing
956 file system or pseudo-filesystem.
957 Options that may be specified:
958 .Bl -tag -width indent
959 .It Cm sync-beg-tid= Ns Ar 0x16llx
960 This is the automatic snapshot access starting transaction id for
962 This parameter is normally updated automatically by the
966 It is important to note that accessing a mirroring slave
967 with a transaction id greater than the last fully synchronized transaction
968 id can result in an unreliable snapshot since you will be accessing
969 data that is still undergoing synchronization.
971 Manually modifying this field is dangerous and can result in a broken mirror.
972 .It Cm sync-end-tid= Ns Ar 0x16llx
973 This is the current synchronization point for mirroring slaves.
974 This parameter is normally updated automatically by the
978 Manually modifying this field is dangerous and can result in a broken mirror.
979 .It Cm shared-uuid= Ns Ar uuid
980 Set the shared UUID for this file system.
981 All mirrors must have the same shared UUID.
982 For safety purposes the
984 directives will refuse to operate on a target with a different shared UUID.
986 Changing the shared UUID on an existing, non-empty mirroring target,
987 including an empty but not completely pruned target,
988 can lead to corruption of the mirroring target.
989 .It Cm unique-uuid= Ns Ar uuid
990 Set the unique UUID for this file system.
991 This UUID should not be used anywhere else,
992 even on exact copies of the file system.
993 .It Cm label= Ns Ar string
994 Set a descriptive label for this file system.
995 .It Cm snapshots= Ns Ar string
996 Specify the snapshots directory which
999 will use to manage this PFS.
1000 .Bl -tag -width indent
1001 .It Nm HAMMER No version 2-
1002 The snapshots directory does not need to be configured for
1003 PFS masters and will default to
1004 .Pa <pfs>/snapshots .
1006 PFS slaves are mirroring slaves so you cannot configure a snapshots
1007 directory on the slave itself to be managed by the slave's machine.
1008 In fact, the slave will likely have a
1010 sub-directory mirrored
1011 from the master, but that directory contains the configuration the master
1012 is using for its copy of the file system, not the configuration that we
1013 want to use for our slave.
1015 It is recommended that
1016 .Pa <fs>/var/slaves/<name>
1017 be configured for a PFS slave, where
1023 is an appropriate label.
1024 .It Nm HAMMER No version 3+
1025 The snapshots directory does not need to be configured for PFS masters or
1027 The snapshots directory defaults to
1028 .Pa /var/hammer/<pfs>
1029 .Pa ( /var/hammer/root
1033 You can control snapshot retention on your slave independent of the master.
1034 .It Cm snapshots-clear
1037 directory path for this PFS.
1038 .It Cm prune-min= Ns Ar N Ns Cm d
1039 .It Cm prune-min= Ns Oo Ar N Ns Cm d/ Oc Ns \
1040 Ar hh Ns Op Cm \&: Ns Ar mm Ns Op Cm \&: Ns Ar ss
1041 Set the minimum fine-grained data retention period.
1043 always retains fine-grained history up to the most recent snapshot.
1044 You can extend the retention period further by specifying a non-zero
1046 Any snapshot softlinks within the retention period are ignored
1047 for the purposes of pruning (the fine grained history is retained).
1048 Number of days, hours, minutes and seconds are given as
1053 Because the transaction id in the snapshot softlink cannot be used
1054 to calculate a timestamp,
1056 uses the earlier of the
1060 field of the softlink to
1061 determine which snapshots fall within the retention period.
1062 Users must be sure to retain one of these two fields when manipulating
1065 .\" ==== pfs-upgrade ====
1066 .It Cm pfs-upgrade Ar dirpath
1067 Upgrade a PFS from slave to master operation.
1068 The PFS will be rolled back to the current end synchronization transaction id
1069 (removing any partial synchronizations), and will then become writable.
1073 currently supports only single masters and using
1074 this command can easily result in file system corruption
1075 if you don't know what you are doing.
1077 This directive will refuse to run if any programs have open descriptors
1078 in the PFS, including programs chdir'd into the PFS.
1079 .\" ==== pfs-downgrade ====
1080 .It Cm pfs-downgrade Ar dirpath
1081 Downgrade a master PFS from master to slave operation.
1082 The PFS becomes read-only and access will be locked to its
1085 This directive will refuse to run if any programs have open descriptors
1086 in the PFS, including programs chdir'd into the PFS.
1087 .\" ==== pfs-destroy ====
1088 .It Cm pfs-destroy Ar dirpath
1089 This permanently destroys a PFS.
1091 This directive will refuse to run if any programs have open descriptors
1092 in the PFS, including programs chdir'd into the PFS.
1093 .\" ==== mirror-read ====
1094 .It Cm mirror-read Ar filesystem Op Ar begin-tid
1095 Generate a mirroring stream to stdout.
1096 The stream ends when the transaction id space has been exhausted.
1097 .\" ==== mirror-read-stream ====
1098 .It Cm mirror-read-stream Ar filesystem Op Ar begin-tid
1099 Generate a mirroring stream to stdout.
1100 Upon completion the stream is paused until new data is synced to the
1103 Operation continues until the pipe is broken.
1106 command for more details.
1107 .\" ==== mirror-write ====
1108 .It Cm mirror-write Ar filesystem
1109 Take a mirroring stream on stdin.
1111 This command will fail if the
1113 configuration field for the two file systems do not match.
1116 command for more details.
1118 If the target PFS does not exist this command will ask you whether
1119 you want to create a compatible PFS slave for the target or not.
1120 .\" ==== mirror-dump ====
1126 to dump an ASCII representation of the mirroring stream.
1127 .\" ==== mirror-copy ====
1128 .\".It Cm mirror-copy Ar [[user@]host:]filesystem [[user@]host:]filesystem
1129 .It Cm mirror-copy \
1130 Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem \
1131 Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem
1132 This is a shortcut which pipes a
1137 If a remote host specification is made the program forks a
1143 on the appropriate host.
1144 The source may be a master or slave PFS, and the target must be a slave PFS.
1146 This command also establishes full duplex communication and turns on
1147 the 2-way protocol feature
1149 which automatically negotiates transaction id
1150 ranges without having to use a cyclefile.
1151 If the operation completes successfully the target PFS's
1154 Note that you must re-chdir into the target PFS to see the updated information.
1155 If you do not you will still be in the previous snapshot.
1157 If the target PFS does not exist this command will ask you whether
1158 you want to create a compatible PFS slave for the target or not.
1159 .\" ==== mirror-stream ====
1160 .\".It Cm mirror-stream Ar [[user@]host:]filesystem [[user@]host:]filesystem
1161 .It Cm mirror-stream \
1162 Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem \
1163 Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem
1164 This is a shortcut which pipes a
1165 .Cm mirror-read-stream
1169 This command works similarly to
1171 but does not exit after the initial mirroring completes.
1172 The mirroring operation will resume as changes continue to be made to the
1174 The command is commonly used with
1178 options to keep the mirroring target in sync with the source on a continuing
1181 If the pipe is broken the command will automatically retry after sleeping
1183 The time slept will be 15 seconds plus the time given in the
1187 This command also detects the initial-mirroring case and spends some
1188 time scanning the B-Tree to find good break points, allowing the initial
1189 bulk mirroring operation to be broken down into 100MB pieces.
1190 This means that the user can kill and restart the operation and it will
1191 not have to start from scratch once it has gotten past the first chunk.
1194 option may be used to change the size of pieces and the
1196 option may be used to disable this feature and perform an initial bulk
1198 .\" ==== version ====
1199 .It Cm version Ar filesystem
1200 This command returns the
1202 file system version for the specified
1204 as well as the range of versions supported in the kernel.
1207 option may be used to remove the summary at the end.
1208 .\" ==== version-upgrade ====
1209 .It Cm version-upgrade Ar filesystem Ar version Op Cm force
1210 This command upgrades the
1215 Once upgraded a file system may not be downgraded.
1216 If you wish to upgrade a file system to a version greater or equal to the
1217 work-in-progress version number you must specify the
1220 Use of WIP versions should be relegated to testing and may require wiping
1221 the file system as development progresses, even though the WIP version might
1225 This command operates on the entire
1227 file system and is not a per PFS operation.
1228 All PFS's will be affected.
1229 .Bl -tag -width indent
1232 default version, first
1237 New directory entry layout.
1238 This version is using a new directory hash key.
1241 New snapshot management, using file system meta-data for saving
1242 configuration file and snapshots (transaction ids etc.).
1243 Also default snapshots directory has changed.
1247 New undo/redo/flush, giving HAMMER a much faster sync and fsync.
1250 .Sh PSEUDO-FILESYSTEM (PFS) NOTES
1251 The root of a PFS is not hooked into the primary
1253 file system as a directory.
1256 creates a special softlink called
1258 (exactly 10 characters long) in the primary
1262 then modifies the contents of the softlink as read by
1264 and thus what you see with an
1266 command or if you were to
1269 If the PFS is a master the link reflects the current state of the PFS.
1270 If the PFS is a slave the link reflects the last completed snapshot, and the
1271 contents of the link will change when the next snapshot is completed, and
1276 utility employs numerous safeties to reduce user foot-shooting.
1279 directive requires that the target be configured as a slave and that the
1281 field of the mirroring source and target match.
1282 .Sh UPGRADE INSTRUCTIONS HAMMER V1 TO V2
1283 This upgrade changes the way directory entries are stored.
1284 It is possible to upgrade a V1 file system to V2 in place, but
1285 directories created prior to the upgrade will continue to use
1288 Note that the slave mirroring code in the target kernel had bugs in
1289 V1 which can create an incompatible root directory on the slave.
1292 master created after the upgrade with a
1294 slave created prior to the upgrade.
1296 Any directories created after upgrading will use a new layout.
1297 .Sh UPGRADE INSTRUCTIONS HAMMER V2 TO V3
1298 This upgrade adds meta-data elements to the B-Tree.
1299 It is possible to upgrade a V2 file system to V3 in place.
1300 After issuing the upgrade be sure to run a
1303 to perform post-upgrade tasks.
1305 After making this upgrade running a
1310 directory for each PFS mount into
1311 .Pa /var/hammer/<pfs> .
1314 root mount will migrate
1317 .Pa /var/hammer/root .
1318 Migration occurs only once and only if you have not specified
1319 a snapshots directory in the PFS configuration.
1320 If you have specified a snapshots directory in the PFS configuration no
1321 automatic migration will occur.
1323 For slaves, if you desire, you can migrate your snapshots
1324 config to the new location manually and then clear the
1325 snapshot directory configuration in the slave PFS.
1326 The new snapshots hierarchy is designed to work with
1327 both master and slave PFSs equally well.
1329 In addition, the old config file will be moved to file system meta-data,
1330 editable via the new
1334 The old config file will be deleted.
1335 Migration occurs only once.
1337 The V3 file system has new
1339 directives for creating snapshots.
1340 All snapshot directives, including the original, will create
1341 meta-data entries for the snapshots and the pruning code will
1342 automatically incorporate these entries into its list and
1343 expire them the same way it expires softlinks.
1344 If you by accident blow away your snapshot softlinks you can use the
1346 directive to get a definitive list from the file system meta-data and
1347 regenerate them from that list.
1352 to backup file systems your scripts may be using the
1354 directive to generate transaction ids.
1355 This directive does not create a snapshot.
1356 You will have to modify your scripts to use the
1358 directive to generate the linkbuf for the softlink you create, or
1359 use one of the other
1364 directive will continue to work as expected and in V3 it will also
1365 record the snapshot transaction id in file system meta-data.
1366 You may also want to make use of the new
1368 tag for the meta-data.
1371 If you used to remove snapshot softlinks with
1373 you should probably start using the
1375 directive instead to also remove the related meta-data.
1376 The pruning code scans the meta-data so just removing the
1377 softlink is not sufficient.
1378 .Sh UPGRADE INSTRUCTIONS HAMMER V3 TO V4
1379 This upgrade changes undo/flush, giving faster sync.
1380 It is possible to upgrade a V3 file system to V4 in place.
1381 This upgrade reformats the UNDO FIFO (typically 1GB), so upgrade might take
1382 a minute or two depending.
1384 Version 4 allows the UNDO FIFO to be flushed without also having
1385 to flush the volume header, removing 2 of the 4 disk syncs typically
1388 and removing 1 of the 2 disk syncs typically
1389 required for a flush sequence.
1390 Version 4 also implements the REDO log (see below) which is capable
1391 of fsync()ing with either one disk flush or zero disk flushes.
1392 .Sh FSYNC FLUSH MODES
1394 implements five different fsync flush modes via the
1395 .Va vfs.hammer.fsync_mode
1398 version 4+ file systems.
1402 fsync mode 3 is set by default.
1403 REDO operation and recovery is enabled by default.
1404 .Bl -tag -width indent
1406 Full synchronous fsync semantics without REDO.
1409 will not generate REDOs.
1412 will completely sync
1413 the data and meta-data and double-flush the FIFO, including
1414 issuing two disk synchronization commands.
1415 The data is guaranteed
1416 to be on the media as of when
1419 Needless to say, this is slow.
1421 Relaxed asynchronous fsync semantics without REDO.
1423 This mode works the same as mode 0 except the last disk synchronization
1424 command is not issued.
1425 It is faster than mode 0 but not even remotely
1426 close to the speed you get with mode 2 or mode 3.
1428 Note that there is no chance of meta-data corruption when using this
1429 mode, it simply means that the data you wrote and then
1431 might not have made it to the media if the storage system crashes at a bad
1435 Full synchronous fsync semantics using REDO.
1436 NOTE: If not running
1437 a HAMMER version 4 filesystem or later mode 0 is silently used.
1440 will generate REDOs in the UNDO/REDO FIFO based on a heuristic.
1441 If this is sufficient to satisfy the
1443 operation the blocks
1444 will be written out and
1446 will wait for the I/Os to complete,
1447 and then followup with a disk sync command to guarantee the data
1448 is on the media before returning.
1449 This is slower than mode 3 and can result in significant disk or
1450 SSDs overheads, though not as bad as mode 0 or mode 1.
1453 Relaxed asynchronous fsync semantics using REDO.
1454 NOTE: If not running
1455 a HAMMER version 4 filesystem or later mode 1 is silently used.
1458 will generate REDOs in the UNDO/REDO FIFO based on a heuristic.
1459 If this is sufficient to satisfy the
1461 operation the blocks
1462 will be written out and
1464 will wait for the I/Os to complete,
1467 issue a disk synchronization command.
1469 Note that there is no chance of meta-data corruption when using this
1470 mode, it simply means that the data you wrote and then
1473 not have made it to the media if the storage system crashes at a bad
1476 This mode is the fastest production fsyncing mode available.
1477 This mode is equivalent to how the UFS fsync in the
1487 This mode is primarily designed
1488 for testing and should not be used on a production system.
1490 .Sh RESTORING FROM A SNAPSHOT BACKUP
1491 You restore a snapshot by copying it over to live, but there is a caveat.
1492 The mtime and atime fields for files accessed via a snapshot is locked
1493 to the ctime in order to keep the snapshot consistent, because neither
1494 mtime nor atime changes roll any history.
1496 In order to avoid unnecessary copying it is recommended that you use
1500 when doing the copyback. Also make sure you traverse the snapshot softlink
1501 by appending a ".", as in "<snapshotpath>/.", and you match up the directory
1506 If the following environment variables exist, they will be used by:
1507 .Bl -tag -width ".Ev EDITOR"
1509 The editor program specified in the variable
1511 will be invoked instead of the default editor, which is
1519 .Bl -tag -width ".It Pa <fs>/var/slaves/<name>" -compact
1520 .It Pa <pfs>/snapshots
1521 default per PFS snapshots directory
1524 .It Pa /var/hammer/<pfs>
1525 default per PFS snapshots directory (not root)
1528 .It Pa /var/hammer/root
1529 default snapshots directory for root directory
1532 .It Pa <snapshots>/config
1539 .It Pa <fs>/var/slaves/<name>
1540 recommended slave PFS snapshots directory
1549 .Xr periodic.conf 5 ,
1550 .Xr mount_hammer 8 ,
1556 utility first appeared in
1559 .An Matthew Dillon Aq dillon@backplane.com
projects / dragonfly.git / blob