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>
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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.
294 This means the free byte count can legally go negative.
296 This command needs the
299 .\" ==== checkmap ====
301 Check the blockmap allocation count.
303 will scan the B-Tree, collect allocation information, and
304 construct a blockmap in-memory. It will then check that blockmap
305 against the on-disk blockmap.
307 This command needs the
311 .It Cm show Op Ar lo Ns Cm \&: Ns Ar objid
313 By default this command will validate all B-Tree
314 linkages and CRCs, including data CRCs, and will report the most verbose
315 information it can dig up.
316 Any errors will show up with a
318 in column 1 along with various
321 If you specify a localization field or a localization:obj_id field,
322 .Ar lo Ns Cm \&: Ns Ar objid ,
324 search for the key printing nodes as it recurses down, and then
325 will iterate forwards.
326 These fields are specified in HEX.
327 Note that the pfsid is the top 16 bits of the 32 bit localization
328 field so PFS #1 would be 00010000.
332 the command will report less information about the inode contents.
336 the command will not report the content of the inode or other typed
341 the command will not report volume header information, big-block fill
342 ratios, mirror transaction ids, or report or check data CRCs.
343 B-Tree CRCs and linkages are still checked.
345 This command needs the
348 .\" ==== show-undo ====
354 This command needs the
358 .\" Dump the B-Tree, record, large-data, and small-data blockmaps, showing
359 .\" physical block assignments and free space percentages.
360 .\" ==== recover ====
361 .It Cm recover Ar targetdir
362 This is a low level command which operates on the filesystem image and
363 attempts to locate and recover files from a corrupted filesystem. The
364 entire image is scanned linearly looking for B-Tree nodes. Any node
365 found which passes its crc test is scanned for file, inode, and directory
366 fragments and the target directory is populated with the resulting data.
367 files and directories in the target directory are initially named after
368 the object id and are renamed as fragmentory information is processed.
370 This command keeps track of filename/objid translations and may eat a
371 considerably amount of memory while operating.
373 This command is literally the last line of defense when it comes to
374 recovering data from a dead filesystem.
375 .\" ==== namekey1 ====
376 .It Cm namekey1 Ar filename
379 64 bit directory hash for the specified file name, using
380 the original directory hash algorithm in version 1 of the file system.
381 The low 32 bits are used as an iterator for hash collisions and will be
383 .\" ==== namekey2 ====
384 .It Cm namekey2 Ar filename
387 64 bit directory hash for the specified file name, using
388 the new directory hash algorithm in version 2 of the file system.
389 The low 32 bits are still used as an iterator but will start out containing
390 part of the hash key.
391 .\" ==== namekey32 ====
392 .It Cm namekey32 Ar filename
393 Generate the top 32 bits of a
395 64 bit directory hash for the specified file name.
398 Shows extended information about all the mounted
401 The information is divided into sections:
402 .Bl -tag -width indent
403 .It Volume identification
404 General information, like the label of the
406 filesystem, the number of volumes it contains, the FSID, and the
409 .It Big block information
410 Big block statistics, such as total, used, reserved and free big blocks.
411 .It Space information
412 Information about space used on the filesystem.
413 Currently total size, used, reserved and free space are displayed.
415 Basic information about the PFSs currently present on a
420 is the ID of the PFS, with 0 being the root PFS.
422 is the current snapshot count on the PFS.
424 displays the mount point of the PFS is currently mounted on (if any).
426 .\" ==== cleanup ====
427 .It Cm cleanup Op Ar filesystem ...
428 This is a meta-command which executes snapshot, prune, rebalance, dedup
429 and reblock commands on the specified
434 is specified this command will clean-up all
436 file systems in use, including PFS's.
437 To do this it will scan all
441 mounts, extract PFS id's, and clean-up each PFS found.
443 This command will access a snapshots
444 directory and a configuration file for each
446 creating them if necessary.
447 .Bl -tag -width indent
448 .It Nm HAMMER No version 2-
449 The configuration file is
451 in the snapshots directory which defaults to
452 .Pa <pfs>/snapshots .
453 .It Nm HAMMER No version 3+
454 The configuration file is saved in file system meta-data, see
457 The snapshots directory defaults to
458 .Pa /var/hammer/<pfs>
459 .Pa ( /var/hammer/root
463 The format of the configuration file is:
464 .Bd -literal -offset indent
465 snapshots <period> <retention-time> [any]
466 prune <period> <max-runtime>
467 rebalance <period> <max-runtime>
468 dedup <period> <max-runtime>
469 reblock <period> <max-runtime>
470 recopy <period> <max-runtime>
474 .Bd -literal -offset indent
475 snapshots 1d 60d # 0d 0d for PFS /tmp, /var/tmp, /usr/obj
483 Time is given with a suffix of
489 meaning day, hour, minute and second.
493 directive has a period of 0 and a retention time of 0
494 then snapshot generation is disabled, removal of old snapshots are
495 disabled, and prunes will use
496 .Cm prune-everything .
500 directive has a period of 0 but a non-zero retention time
501 then this command will not create any new snapshots but will remove old
502 snapshots it finds based on the retention time. This form should be
503 used on PFS masters where you are generating your own snapshot softlinks
504 manually and on PFS slaves when all you wish to do is prune away existing
505 snapshots inherited via the mirroring stream.
507 By default only snapshots in the form
508 .Ql snap- Ns Ar yyyymmdd Ns Op - Ns Ar HHMM
512 directive is specified as a third argument on the
514 config line then any softlink of the form
515 .Ql *- Ns Ar yyyymmdd Ns Op - Ns Ar HHMM
517 .Ql *. Ns Ar yyyymmdd Ns Op - Ns Ar HHMM
520 A prune max-runtime of 0 means unlimited.
522 If period hasn't passed since the previous
525 For example a day has passed when midnight is passed (localtime).
533 The default configuration file will create a daily snapshot, do a daily
534 pruning, rebalancing, deduping and reblocking run and a monthly recopy run.
535 Reblocking is defragmentation with a level of 95%,
536 and recopy is full defragmentation.
538 By default prune and rebalance operations are time limited to 5 minutes,
539 dedup and reblock operations to a bit over 5 minutes,
540 and recopy operations to a bit over 10 minutes.
541 Reblocking and recopy runs are each broken down into four separate functions:
542 btree, inodes, dirs and data.
543 Each function is time limited to the time given in the configuration file,
544 but the btree, inodes and dirs functions usually does not take very long time,
545 full defragmentation is always used for these three functions.
546 Also note that this directive will by default disable snapshots on
553 The defaults may be adjusted by modifying the configuration file.
554 The pruning and reblocking commands automatically maintain a cyclefile
555 for incremental operation.
556 If you interrupt (^C) the program the cyclefile will be updated,
558 may continue to run in the background for a few seconds until the
560 ioctl detects the interrupt.
563 PFS option can be set to use another location for the snapshots directory.
565 Work on this command is still in progress.
567 An ability to remove snapshots dynamically as the
568 file system becomes full.
570 .It Cm config Op Ar filesystem Op Ar configfile
573 Show or change configuration for
575 If zero or one arguments are specified this function dumps the current
576 configuration file to stdout.
577 Zero arguments specifies the PFS containing the current directory.
578 This configuration file is stored in file system meta-data.
579 If two arguments are specified this function installs a new config file.
583 versions less than 3 the configuration file is by default stored in
584 .Pa <pfs>/snapshots/config ,
585 but in all later versions the configuration file is stored in file system
587 .\" ==== viconfig ====
588 .It Cm viconfig Op Ar filesystem
591 Edit the configuration file and reinstall into file system meta-data when done.
592 Zero arguments specifies the PFS containing the current directory.
593 .\" ==== volume-add ====
594 .It Cm volume-add Ar device Ar filesystem
595 This command will format
597 and add all of its space to
601 All existing data contained on
603 will be destroyed by this operation!
608 file system, formatting will be denied.
609 You can overcome this sanity check
612 to erase the beginning sectors of the device.
613 Also remember that you have to specify
615 together with any other device that make up the file system,
620 .\" ==== volume-del ====
621 .It Cm volume-del Ar device Ar filesystem
622 This command will remove volume
627 Remember that you have to remove
629 from the colon-separated list in
633 .\" ==== volume-list ====
634 .It Cm volume-list Ar filesystem
635 This command will list the volumes that make up
637 .\" ==== snapshot ====
638 .It Cm snapshot Oo Ar filesystem Oc Ar snapshot-dir
639 .It Cm snapshot Ar filesystem Ar snapshot-dir Op Ar note
640 Takes a snapshot of the file system either explicitly given by
642 or implicitly derived from the
644 argument and creates a symlink in the directory provided by
646 pointing to the snapshot.
649 is not a directory, it is assumed to be a format string passed to
651 with the current time as parameter.
654 refers to an existing directory, a default format string of
656 is assumed and used as name for the newly created symlink.
658 Snapshot is a per PFS operation, so a
660 file system and each PFS in it have to be snapshot separately.
662 Example, assuming that
670 are file systems on their own, the following invocations:
671 .Bd -literal -offset indent
672 hammer snapshot /mysnapshots
674 hammer snapshot /mysnapshots/%Y-%m-%d
676 hammer snapshot /obj /mysnapshots/obj-%Y-%m-%d
678 hammer snapshot /usr /my/snaps/usr "note"
681 Would create symlinks similar to:
682 .Bd -literal -offset indent
683 /mysnapshots/snap-20080627-1210 -> /@@0x10d2cd05b7270d16
685 /mysnapshots/2008-06-27 -> /@@0x10d2cd05b7270d16
687 /mysnapshots/obj-2008-06-27 -> /obj@@0x10d2cd05b7270d16
689 /my/snaps/usr/snap-20080627-1210 -> /usr@@0x10d2cd05b7270d16
694 version 3+ file system the snapshot is also recorded in file system meta-data
695 along with the optional
701 .It Cm snap Ar path Op Ar note
704 Create a snapshot for the PFS containing
706 and create a snapshot softlink.
707 If the path specified is a
708 directory a standard snapshot softlink will be created in the directory.
709 The snapshot softlink points to the base of the mounted PFS.
710 .It Cm snaplo Ar path Op Ar note
713 Create a snapshot for the PFS containing
715 and create a snapshot softlink.
716 If the path specified is a
717 directory a standard snapshot softlink will be created in the directory.
718 The snapshot softlink points into the directory it is contained in.
719 .It Cm snapq Ar dir Op Ar note
722 Create a snapshot for the PFS containing the specified directory but do
723 not create a softlink.
724 Instead output a path which can be used to access
725 the directory via the snapshot.
727 An absolute or relative path may be specified.
728 The path will be used as-is as a prefix in the path output to stdout.
730 snap and snapshot directives the snapshot transaction id will be registered
731 in the file system meta-data.
732 .It Cm snaprm Ar path Ar ...
733 .It Cm snaprm Ar transid Ar ...
734 .It Cm snaprm Ar filesystem Ar transid Ar ...
737 Remove a snapshot given its softlink or transaction id.
738 If specifying a transaction id
739 the snapshot is removed from file system meta-data but you are responsible
740 for removing any related softlinks.
742 If a softlink path is specified the filesystem and transaction id
743 is derived from the contents of the softlink.
744 If just a transaction id is specified it is assumed to be a snapshot
745 in the HAMMER filesystem you are currently chdir'd into.
746 You can also specify the filesystem and transaction id explicitly.
747 .It Cm snapls Op Ar path ...
750 Dump the snapshot meta-data for PFSs containing each
752 listing all available snapshots and their notes.
753 If no arguments are specified snapshots for the PFS containing the
754 current directory are listed.
755 This is the definitive list of snapshots for the file system.
757 .It Cm prune Ar softlink-dir
758 Prune the file system based on previously created snapshot softlinks.
759 Pruning is the act of deleting file system history.
762 command will delete file system history such that
763 the file system state is retained for the given snapshots,
764 and all history after the latest snapshot.
765 By setting the per PFS parameter
767 history is guaranteed to be saved at least this time interval.
768 All other history is deleted.
770 The target directory is expected to contain softlinks pointing to
771 snapshots of the file systems you wish to retain.
772 The directory is scanned non-recursively and the mount points and
773 transaction ids stored in the softlinks are extracted and sorted.
774 The file system is then explicitly pruned according to what is found.
775 Cleaning out portions of the file system is as simple as removing a
776 snapshot softlink and then running the
780 As a safety measure pruning only occurs if one or more softlinks are found
783 snapshot id extension.
784 Currently the scanned softlink directory must contain softlinks pointing
788 The softlinks may specify absolute or relative paths.
789 Softlinks must use 20-character
791 transaction ids, as might be returned from
792 .Nm Cm synctid Ar filesystem .
794 Pruning is a per PFS operation, so a
796 file system and each PFS in it have to be pruned separately.
798 Note that pruning a file system may not immediately free-up space,
799 though typically some space will be freed if a large number of records are
801 The file system must be reblocked to completely recover all available space.
803 Example, lets say your that you didn't set
805 and snapshot directory contains the following links:
806 .Bd -literal -offset indent
807 lrwxr-xr-x 1 root wheel 29 May 31 17:57 snap1 ->
808 /usr/obj/@@0x10d2cd05b7270d16
810 lrwxr-xr-x 1 root wheel 29 May 31 17:58 snap2 ->
811 /usr/obj/@@0x10d2cd13f3fde98f
813 lrwxr-xr-x 1 root wheel 29 May 31 17:59 snap3 ->
814 /usr/obj/@@0x10d2cd222adee364
817 If you were to run the
819 command on this directory, then the
822 mount will be pruned to retain the above three snapshots.
823 In addition, history for modifications made to the file system older than
824 the oldest snapshot will be destroyed and history for potentially fine-grained
825 modifications made to the file system more recently than the most recent
826 snapshot will be retained.
828 If you then delete the
830 softlink and rerun the
833 history for modifications pertaining to that snapshot would be destroyed.
837 file system versions 3+ this command also scans the snapshots stored
838 in the file system meta-data and includes them in the prune.
839 .\" ==== prune-everything ====
840 .It Cm prune-everything Ar filesystem
841 This command will remove all historical records from the file system.
842 This directive is not normally used on a production system.
844 This command does not remove snapshot softlinks but will delete all
845 snapshots recorded in file system meta-data (for file system version 3+).
846 The user is responsible for deleting any softlinks.
848 Pruning is a per PFS operation, so a
850 file system and each PFS in it have to be pruned separately.
851 .\" ==== rebalance ====
852 .It Cm rebalance Ar filesystem Op Ar saturation_percentage
853 This command will rebalance the B-Tree, nodes with small number of
854 elements will be combined and element counts will be smoothed out
857 The saturation percentage is between 50% and 100%.
858 The default is 75% (the
860 suffix is not needed).
862 Rebalancing is a per PFS operation, so a
864 file system and each PFS in it have to be rebalanced separately.
866 .It Cm dedup Ar filesystem
869 Perform offline (post-process) deduplication. Deduplication occurs at
870 the block level, currently only data blocks of the same size can be
871 deduped, metadata blocks can not. The hash function used for comparing
872 data blocks is CRC-32 (CRCs are computed anyways as part of
874 data integrity features, so there's no additional overhead). Since CRC
875 is a weak hash function a byte-by-byte comparison is done before actual
876 deduping. In case of a CRC collision (two data blocks have the same CRC
877 but different contents) the checksum is upgraded to SHA-256.
881 reblocker may partially blow up (re-expand) dedup (reblocker's normal
882 operation is to reallocate every record, so it's possible for deduped
883 blocks to be re-expanded back).
885 Deduplication is a per PFS operation, so a
887 file system and each PFS in it have to be deduped separately. This also
888 means that if you have duplicated data in two different PFSs that data
889 won't be deduped, however the addition of such feature is planned.
890 .\" ==== dedup-simulate ====
891 .It Cm dedup-simulate Ar filesystem
894 Shows potential space savings (simulated dedup ratio) one can get after
897 command. If the estimated dedup ratio is greater than 1.00 you will see
898 dedup space savings. Remember that this is an estimated number, in
899 practice real dedup ratio will be slightly smaller because of
901 bigblock underflows, B-Tree locking issues and other factors.
902 .\" ==== reblock* ====
903 .It Cm reblock Ar filesystem Op Ar fill_percentage
904 .It Cm reblock-btree Ar filesystem Op Ar fill_percentage
905 .It Cm reblock-inodes Ar filesystem Op Ar fill_percentage
906 .It Cm reblock-dirs Ar filesystem Op Ar fill_percentage
907 .It Cm reblock-data Ar filesystem Op Ar fill_percentage
908 Attempt to defragment and free space for reuse by reblocking a live
911 Big-blocks cannot be reused by
913 until they are completely free.
914 This command also has the effect of reordering all elements, effectively
915 defragmenting the file system.
917 The default fill percentage is 100% and will cause the file system to be
918 completely defragmented.
919 All specified element types will be reallocated and rewritten.
920 If you wish to quickly free up space instead try specifying
921 a smaller fill percentage, such as 90% or 80% (the
923 suffix is not needed).
925 Since this command may rewrite the entire contents of the disk it is
926 best to do it incrementally from a
932 options to limit the run time.
933 The file system would thus be defragmented over long period of time.
935 It is recommended that separate invocations be used for each data type.
936 B-Tree nodes, inodes, and directories are typically the most important
937 elements needing defragmentation.
938 Data can be defragmented over a longer period of time.
940 Reblocking is a per PFS operation, so a
942 file system and each PFS in it have to be reblocked separately.
943 .\" ==== pfs-status ====
944 .It Cm pfs-status Ar dirpath ...
945 Retrieve the mirroring configuration parameters for the specified
947 file systems or pseudo-filesystems (PFS's).
948 .\" ==== pfs-master ====
949 .It Cm pfs-master Ar dirpath Op Ar options
950 Create a pseudo-filesystem (PFS) inside a
953 Up to 65535 such file systems can be created.
954 Each PFS uses an independent inode numbering space making it suitable
955 for use as a replication source or target.
959 directive creates a PFS that you can read, write, and use as a mirroring
962 It is recommended to use a
964 mount to access a PFS, for more information see
966 .\" ==== pfs-slave ====
967 .It Cm pfs-slave Ar dirpath Op Ar options
968 Create a pseudo-filesystem (PFS) inside a
971 Up to 65535 such file systems can be created.
972 Each PFS uses an independent inode numbering space making it suitable
973 for use as a replication source or target.
977 directive creates a PFS that you can use as a mirroring target.
978 You will not be able to access a slave PFS until you have completed the
979 first mirroring operation with it as the target (its root directory will
980 not exist until then).
982 Access to the pfs-slave via the special softlink, as described in the
987 dynamically modify the snapshot transaction id by returning a dynamic result
992 A PFS can only be truly destroyed with the
995 Removing the softlink will not destroy the underlying PFS.
997 It is recommended to use a
999 mount to access a PFS, for more information see
1001 .\" ==== pfs-update ====
1002 .It Cm pfs-update Ar dirpath Op Ar options
1003 Update the configuration parameters for an existing
1005 file system or pseudo-filesystem.
1006 Options that may be specified:
1007 .Bl -tag -width indent
1008 .It Cm sync-beg-tid= Ns Ar 0x16llx
1009 This is the automatic snapshot access starting transaction id for
1011 This parameter is normally updated automatically by the
1015 It is important to note that accessing a mirroring slave
1016 with a transaction id greater than the last fully synchronized transaction
1017 id can result in an unreliable snapshot since you will be accessing
1018 data that is still undergoing synchronization.
1020 Manually modifying this field is dangerous and can result in a broken mirror.
1021 .It Cm sync-end-tid= Ns Ar 0x16llx
1022 This is the current synchronization point for mirroring slaves.
1023 This parameter is normally updated automatically by the
1027 Manually modifying this field is dangerous and can result in a broken mirror.
1028 .It Cm shared-uuid= Ns Ar uuid
1029 Set the shared UUID for this file system.
1030 All mirrors must have the same shared UUID.
1031 For safety purposes the
1033 directives will refuse to operate on a target with a different shared UUID.
1035 Changing the shared UUID on an existing, non-empty mirroring target,
1036 including an empty but not completely pruned target,
1037 can lead to corruption of the mirroring target.
1038 .It Cm unique-uuid= Ns Ar uuid
1039 Set the unique UUID for this file system.
1040 This UUID should not be used anywhere else,
1041 even on exact copies of the file system.
1042 .It Cm label= Ns Ar string
1043 Set a descriptive label for this file system.
1044 .It Cm snapshots= Ns Ar string
1045 Specify the snapshots directory which
1048 will use to manage this PFS.
1049 .Bl -tag -width indent
1050 .It Nm HAMMER No version 2-
1051 The snapshots directory does not need to be configured for
1052 PFS masters and will default to
1053 .Pa <pfs>/snapshots .
1055 PFS slaves are mirroring slaves so you cannot configure a snapshots
1056 directory on the slave itself to be managed by the slave's machine.
1057 In fact, the slave will likely have a
1059 sub-directory mirrored
1060 from the master, but that directory contains the configuration the master
1061 is using for its copy of the file system, not the configuration that we
1062 want to use for our slave.
1064 It is recommended that
1065 .Pa <fs>/var/slaves/<name>
1066 be configured for a PFS slave, where
1072 is an appropriate label.
1073 .It Nm HAMMER No version 3+
1074 The snapshots directory does not need to be configured for PFS masters or
1076 The snapshots directory defaults to
1077 .Pa /var/hammer/<pfs>
1078 .Pa ( /var/hammer/root
1082 You can control snapshot retention on your slave independent of the master.
1083 .It Cm snapshots-clear
1086 directory path for this PFS.
1087 .It Cm prune-min= Ns Ar N Ns Cm d
1088 .It Cm prune-min= Ns Oo Ar N Ns Cm d/ Oc Ns \
1089 Ar hh Ns Op Cm \&: Ns Ar mm Ns Op Cm \&: Ns Ar ss
1090 Set the minimum fine-grained data retention period.
1092 always retains fine-grained history up to the most recent snapshot.
1093 You can extend the retention period further by specifying a non-zero
1095 Any snapshot softlinks within the retention period are ignored
1096 for the purposes of pruning (the fine grained history is retained).
1097 Number of days, hours, minutes and seconds are given as
1102 Because the transaction id in the snapshot softlink cannot be used
1103 to calculate a timestamp,
1105 uses the earlier of the
1109 field of the softlink to
1110 determine which snapshots fall within the retention period.
1111 Users must be sure to retain one of these two fields when manipulating
1114 .\" ==== pfs-upgrade ====
1115 .It Cm pfs-upgrade Ar dirpath
1116 Upgrade a PFS from slave to master operation.
1117 The PFS will be rolled back to the current end synchronization transaction id
1118 (removing any partial synchronizations), and will then become writable.
1122 currently supports only single masters and using
1123 this command can easily result in file system corruption
1124 if you don't know what you are doing.
1126 This directive will refuse to run if any programs have open descriptors
1127 in the PFS, including programs chdir'd into the PFS.
1128 .\" ==== pfs-downgrade ====
1129 .It Cm pfs-downgrade Ar dirpath
1130 Downgrade a master PFS from master to slave operation.
1131 The PFS becomes read-only and access will be locked to its
1134 This directive will refuse to run if any programs have open descriptors
1135 in the PFS, including programs chdir'd into the PFS.
1136 .\" ==== pfs-destroy ====
1137 .It Cm pfs-destroy Ar dirpath
1138 This permanently destroys a PFS.
1140 This directive will refuse to run if any programs have open descriptors
1141 in the PFS, including programs chdir'd into the PFS.
1142 .\" ==== mirror-read ====
1143 .It Cm mirror-read Ar filesystem Op Ar begin-tid
1144 Generate a mirroring stream to stdout.
1145 The stream ends when the transaction id space has been exhausted.
1146 .\" ==== mirror-read-stream ====
1147 .It Cm mirror-read-stream Ar filesystem Op Ar begin-tid
1148 Generate a mirroring stream to stdout.
1149 Upon completion the stream is paused until new data is synced to the
1152 Operation continues until the pipe is broken.
1155 command for more details.
1156 .\" ==== mirror-write ====
1157 .It Cm mirror-write Ar filesystem
1158 Take a mirroring stream on stdin.
1160 This command will fail if the
1162 configuration field for the two file systems do not match.
1165 command for more details.
1167 If the target PFS does not exist this command will ask you whether
1168 you want to create a compatible PFS slave for the target or not.
1169 .\" ==== mirror-dump ====
1175 to dump an ASCII representation of the mirroring stream.
1176 .\" ==== mirror-copy ====
1177 .\".It Cm mirror-copy Ar [[user@]host:]filesystem [[user@]host:]filesystem
1178 .It Cm mirror-copy \
1179 Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem \
1180 Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem
1181 This is a shortcut which pipes a
1186 If a remote host specification is made the program forks a
1192 on the appropriate host.
1193 The source may be a master or slave PFS, and the target must be a slave PFS.
1195 This command also establishes full duplex communication and turns on
1196 the 2-way protocol feature
1198 which automatically negotiates transaction id
1199 ranges without having to use a cyclefile.
1200 If the operation completes successfully the target PFS's
1203 Note that you must re-chdir into the target PFS to see the updated information.
1204 If you do not you will still be in the previous snapshot.
1206 If the target PFS does not exist this command will ask you whether
1207 you want to create a compatible PFS slave for the target or not.
1208 .\" ==== mirror-stream ====
1209 .\".It Cm mirror-stream Ar [[user@]host:]filesystem [[user@]host:]filesystem
1210 .It Cm mirror-stream \
1211 Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem \
1212 Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem
1213 This is a shortcut which pipes a
1214 .Cm mirror-read-stream
1218 This command works similarly to
1220 but does not exit after the initial mirroring completes.
1221 The mirroring operation will resume as changes continue to be made to the
1223 The command is commonly used with
1227 options to keep the mirroring target in sync with the source on a continuing
1230 If the pipe is broken the command will automatically retry after sleeping
1232 The time slept will be 15 seconds plus the time given in the
1236 This command also detects the initial-mirroring case and spends some
1237 time scanning the B-Tree to find good break points, allowing the initial
1238 bulk mirroring operation to be broken down into 100MB pieces.
1239 This means that the user can kill and restart the operation and it will
1240 not have to start from scratch once it has gotten past the first chunk.
1243 option may be used to change the size of pieces and the
1245 option may be used to disable this feature and perform an initial bulk
1247 .\" ==== version ====
1248 .It Cm version Ar filesystem
1249 This command returns the
1251 file system version for the specified
1253 as well as the range of versions supported in the kernel.
1256 option may be used to remove the summary at the end.
1257 .\" ==== version-upgrade ====
1258 .It Cm version-upgrade Ar filesystem Ar version Op Cm force
1259 This command upgrades the
1264 Once upgraded a file system may not be downgraded.
1265 If you wish to upgrade a file system to a version greater or equal to the
1266 work-in-progress version number you must specify the
1269 Use of WIP versions should be relegated to testing and may require wiping
1270 the file system as development progresses, even though the WIP version might
1274 This command operates on the entire
1276 file system and is not a per PFS operation.
1277 All PFS's will be affected.
1278 .Bl -tag -width indent
1281 default version, first
1286 New directory entry layout.
1287 This version is using a new directory hash key.
1290 New snapshot management, using file system meta-data for saving
1291 configuration file and snapshots (transaction ids etc.).
1292 Also default snapshots directory has changed.
1296 New undo/redo/flush, giving HAMMER a much faster sync and fsync.
1299 .Sh PSEUDO-FILESYSTEM (PFS) NOTES
1300 The root of a PFS is not hooked into the primary
1302 file system as a directory.
1305 creates a special softlink called
1307 (exactly 10 characters long) in the primary
1311 then modifies the contents of the softlink as read by
1313 and thus what you see with an
1315 command or if you were to
1318 If the PFS is a master the link reflects the current state of the PFS.
1319 If the PFS is a slave the link reflects the last completed snapshot, and the
1320 contents of the link will change when the next snapshot is completed, and
1325 utility employs numerous safeties to reduce user foot-shooting.
1328 directive requires that the target be configured as a slave and that the
1330 field of the mirroring source and target match.
1331 .Sh UPGRADE INSTRUCTIONS HAMMER V1 TO V2
1332 This upgrade changes the way directory entries are stored.
1333 It is possible to upgrade a V1 file system to V2 in place, but
1334 directories created prior to the upgrade will continue to use
1337 Note that the slave mirroring code in the target kernel had bugs in
1338 V1 which can create an incompatible root directory on the slave.
1341 master created after the upgrade with a
1343 slave created prior to the upgrade.
1345 Any directories created after upgrading will use a new layout.
1346 .Sh UPGRADE INSTRUCTIONS HAMMER V2 TO V3
1347 This upgrade adds meta-data elements to the B-Tree.
1348 It is possible to upgrade a V2 file system to V3 in place.
1349 After issuing the upgrade be sure to run a
1352 to perform post-upgrade tasks.
1354 After making this upgrade running a
1359 directory for each PFS mount into
1360 .Pa /var/hammer/<pfs> .
1363 root mount will migrate
1366 .Pa /var/hammer/root .
1367 Migration occurs only once and only if you have not specified
1368 a snapshots directory in the PFS configuration.
1369 If you have specified a snapshots directory in the PFS configuration no
1370 automatic migration will occur.
1372 For slaves, if you desire, you can migrate your snapshots
1373 config to the new location manually and then clear the
1374 snapshot directory configuration in the slave PFS.
1375 The new snapshots hierarchy is designed to work with
1376 both master and slave PFSs equally well.
1378 In addition, the old config file will be moved to file system meta-data,
1379 editable via the new
1383 The old config file will be deleted.
1384 Migration occurs only once.
1386 The V3 file system has new
1388 directives for creating snapshots.
1389 All snapshot directives, including the original, will create
1390 meta-data entries for the snapshots and the pruning code will
1391 automatically incorporate these entries into its list and
1392 expire them the same way it expires softlinks.
1393 If you by accident blow away your snapshot softlinks you can use the
1395 directive to get a definitive list from the file system meta-data and
1396 regenerate them from that list.
1401 to backup file systems your scripts may be using the
1403 directive to generate transaction ids.
1404 This directive does not create a snapshot.
1405 You will have to modify your scripts to use the
1407 directive to generate the linkbuf for the softlink you create, or
1408 use one of the other
1413 directive will continue to work as expected and in V3 it will also
1414 record the snapshot transaction id in file system meta-data.
1415 You may also want to make use of the new
1417 tag for the meta-data.
1420 If you used to remove snapshot softlinks with
1422 you should probably start using the
1424 directive instead to also remove the related meta-data.
1425 The pruning code scans the meta-data so just removing the
1426 softlink is not sufficient.
1427 .Sh UPGRADE INSTRUCTIONS HAMMER V3 TO V4
1428 This upgrade changes undo/flush, giving faster sync.
1429 It is possible to upgrade a V3 file system to V4 in place.
1430 This upgrade reformats the UNDO FIFO (typically 1GB), so upgrade might take
1431 a minute or two depending.
1433 Version 4 allows the UNDO FIFO to be flushed without also having
1434 to flush the volume header, removing 2 of the 4 disk syncs typically
1437 and removing 1 of the 2 disk syncs typically
1438 required for a flush sequence.
1439 Version 4 also implements the REDO log (see below) which is capable
1440 of fsync()ing with either one disk flush or zero disk flushes.
1441 .Sh FSYNC FLUSH MODES
1443 implements five different fsync flush modes via the
1444 .Va vfs.hammer.fsync_mode
1447 version 4+ file systems.
1451 fsync mode 3 is set by default.
1452 REDO operation and recovery is enabled by default.
1453 .Bl -tag -width indent
1455 Full synchronous fsync semantics without REDO.
1458 will not generate REDOs.
1461 will completely sync
1462 the data and meta-data and double-flush the FIFO, including
1463 issuing two disk synchronization commands.
1464 The data is guaranteed
1465 to be on the media as of when
1468 Needless to say, this is slow.
1470 Relaxed asynchronous fsync semantics without REDO.
1472 This mode works the same as mode 0 except the last disk synchronization
1473 command is not issued.
1474 It is faster than mode 0 but not even remotely
1475 close to the speed you get with mode 2 or mode 3.
1477 Note that there is no chance of meta-data corruption when using this
1478 mode, it simply means that the data you wrote and then
1480 might not have made it to the media if the storage system crashes at a bad
1484 Full synchronous fsync semantics using REDO.
1485 NOTE: If not running
1486 a HAMMER version 4 filesystem or later mode 0 is silently used.
1489 will generate REDOs in the UNDO/REDO FIFO based on a heuristic.
1490 If this is sufficient to satisfy the
1492 operation the blocks
1493 will be written out and
1495 will wait for the I/Os to complete,
1496 and then followup with a disk sync command to guarantee the data
1497 is on the media before returning.
1498 This is slower than mode 3 and can result in significant disk or
1499 SSDs overheads, though not as bad as mode 0 or mode 1.
1502 Relaxed asynchronous fsync semantics using REDO.
1503 NOTE: If not running
1504 a HAMMER version 4 filesystem or later mode 1 is silently used.
1507 will generate REDOs in the UNDO/REDO FIFO based on a heuristic.
1508 If this is sufficient to satisfy the
1510 operation the blocks
1511 will be written out and
1513 will wait for the I/Os to complete,
1516 issue a disk synchronization command.
1518 Note that there is no chance of meta-data corruption when using this
1519 mode, it simply means that the data you wrote and then
1522 not have made it to the media if the storage system crashes at a bad
1525 This mode is the fastest production fsyncing mode available.
1526 This mode is equivalent to how the UFS fsync in the
1536 This mode is primarily designed
1537 for testing and should not be used on a production system.
1539 .Sh RESTORING FROM A SNAPSHOT BACKUP
1540 You restore a snapshot by copying it over to live, but there is a caveat.
1541 The mtime and atime fields for files accessed via a snapshot is locked
1542 to the ctime in order to keep the snapshot consistent, because neither
1543 mtime nor atime changes roll any history.
1545 In order to avoid unnecessary copying it is recommended that you use
1549 when doing the copyback. Also make sure you traverse the snapshot softlink
1550 by appending a ".", as in "<snapshotpath>/.", and you match up the directory
1555 If the following environment variables exist, they will be used by:
1556 .Bl -tag -width ".Ev EDITOR"
1558 The editor program specified in the variable
1560 will be invoked instead of the default editor, which is
1568 .Bl -tag -width ".It Pa <fs>/var/slaves/<name>" -compact
1569 .It Pa <pfs>/snapshots
1570 default per PFS snapshots directory
1573 .It Pa /var/hammer/<pfs>
1574 default per PFS snapshots directory (not root)
1577 .It Pa /var/hammer/root
1578 default snapshots directory for root directory
1581 .It Pa <snapshots>/config
1588 .It Pa <fs>/var/slaves/<name>
1589 recommended slave PFS snapshots directory
1598 .Xr periodic.conf 5 ,
1599 .Xr mount_hammer 8 ,
1605 utility first appeared in
1608 .An Matthew Dillon Aq dillon@backplane.com
projects / dragonfly.git / blob