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 .
499 directive has a period of 0 but a non-zero retention time
500 then this command will not create any new snapshots but will remove old
501 snapshots it finds based on the retention time.
503 By default only snapshots in the form
504 .Ql snap- Ns Ar yyyymmdd Ns Op - Ns Ar HHMM
508 directive is specified as a third argument on the
510 config line then any softlink of the form
511 .Ql *- Ns Ar yyyymmdd Ns Op - Ns Ar HHMM
513 .Ql *. Ns Ar yyyymmdd Ns Op - Ns Ar HHMM
516 A prune max-runtime of 0 means unlimited.
518 If period hasn't passed since the previous
521 For example a day has passed when midnight is passed (localtime).
529 The default configuration file will create a daily snapshot, do a daily
530 pruning, rebalancing, deduping and reblocking run and a monthly recopy run.
531 Reblocking is defragmentation with a level of 95%,
532 and recopy is full defragmentation.
534 By default prune and rebalance operations are time limited to 5 minutes,
535 dedup and reblock operations to a bit over 5 minutes,
536 and recopy operations to a bit over 10 minutes.
537 Reblocking and recopy runs are each broken down into four separate functions:
538 btree, inodes, dirs and data.
539 Each function is time limited to the time given in the configuration file,
540 but the btree, inodes and dirs functions usually does not take very long time,
541 full defragmentation is always used for these three functions.
542 Also note that this directive will by default disable snapshots on
549 The defaults may be adjusted by modifying the configuration file.
550 The pruning and reblocking commands automatically maintain a cyclefile
551 for incremental operation.
552 If you interrupt (^C) the program the cyclefile will be updated,
554 may continue to run in the background for a few seconds until the
556 ioctl detects the interrupt.
559 PFS option can be set to use another location for the snapshots directory.
561 Work on this command is still in progress.
563 An ability to remove snapshots dynamically as the
564 file system becomes full.
566 .It Cm config Op Ar filesystem Op Ar configfile
569 Show or change configuration for
571 If zero or one arguments are specified this function dumps the current
572 configuration file to stdout.
573 Zero arguments specifies the PFS containing the current directory.
574 This configuration file is stored in file system meta-data.
575 If two arguments are specified this function installs a new config file.
579 versions less than 3 the configuration file is by default stored in
580 .Pa <pfs>/snapshots/config ,
581 but in all later versions the configuration file is stored in file system
583 .\" ==== viconfig ====
584 .It Cm viconfig Op Ar filesystem
587 Edit the configuration file and reinstall into file system meta-data when done.
588 Zero arguments specifies the PFS containing the current directory.
589 .\" ==== volume-add ====
590 .It Cm volume-add Ar device Ar filesystem
591 This command will format
593 and add all of its space to
597 All existing data contained on
599 will be destroyed by this operation!
604 file system, formatting will be denied.
605 You can overcome this sanity check
608 to erase the beginning sectors of the device.
609 Also remember that you have to specify
611 together with any other device that make up the file system,
616 .\" ==== volume-del ====
617 .It Cm volume-del Ar device Ar filesystem
618 This command will remove volume
623 Remember that you have to remove
625 from the colon-separated list in
629 .\" ==== snapshot ====
630 .It Cm snapshot Oo Ar filesystem Oc Ar snapshot-dir
631 .It Cm snapshot Ar filesystem Ar snapshot-dir Op Ar note
632 Takes a snapshot of the file system either explicitly given by
634 or implicitly derived from the
636 argument and creates a symlink in the directory provided by
638 pointing to the snapshot.
641 is not a directory, it is assumed to be a format string passed to
643 with the current time as parameter.
646 refers to an existing directory, a default format string of
648 is assumed and used as name for the newly created symlink.
650 Snapshot is a per PFS operation, so a
652 file system and each PFS in it have to be snapshot separately.
654 Example, assuming that
662 are file systems on their own, the following invocations:
663 .Bd -literal -offset indent
664 hammer snapshot /mysnapshots
666 hammer snapshot /mysnapshots/%Y-%m-%d
668 hammer snapshot /obj /mysnapshots/obj-%Y-%m-%d
670 hammer snapshot /usr /my/snaps/usr "note"
673 Would create symlinks similar to:
674 .Bd -literal -offset indent
675 /mysnapshots/snap-20080627-1210 -> /@@0x10d2cd05b7270d16
677 /mysnapshots/2008-06-27 -> /@@0x10d2cd05b7270d16
679 /mysnapshots/obj-2008-06-27 -> /obj@@0x10d2cd05b7270d16
681 /my/snaps/usr/snap-20080627-1210 -> /usr@@0x10d2cd05b7270d16
686 version 3+ file system the snapshot is also recorded in file system meta-data
687 along with the optional
693 .It Cm snap Ar path Op Ar note
696 Create a snapshot for the PFS containing
698 and create a snapshot softlink.
699 If the path specified is a
700 directory a standard snapshot softlink will be created in the directory.
701 The snapshot softlink points to the base of the mounted PFS.
702 .It Cm snaplo Ar path Op Ar note
705 Create a snapshot for the PFS containing
707 and create a snapshot softlink.
708 If the path specified is a
709 directory a standard snapshot softlink will be created in the directory.
710 The snapshot softlink points into the directory it is contained in.
711 .It Cm snapq Ar dir Op Ar note
714 Create a snapshot for the PFS containing the specified directory but do
715 not create a softlink.
716 Instead output a path which can be used to access
717 the directory via the snapshot.
719 An absolute or relative path may be specified.
720 The path will be used as-is as a prefix in the path output to stdout.
722 snap and snapshot directives the snapshot transaction id will be registered
723 in the file system meta-data.
724 .It Cm snaprm Ar path Ar ...
725 .It Cm snaprm Ar transid Ar ...
726 .It Cm snaprm Ar filesystem Ar transid Ar ...
729 Remove a snapshot given its softlink or transaction id.
730 If specifying a transaction id
731 the snapshot is removed from file system meta-data but you are responsible
732 for removing any related softlinks.
734 If a softlink path is specified the filesystem and transaction id
735 is derived from the contents of the softlink.
736 If just a transaction id is specified it is assumed to be a snapshot
737 in the HAMMER filesystem you are currently chdir'd into.
738 You can also specify the filesystem and transaction id explicitly.
739 .It Cm snapls Op Ar path ...
742 Dump the snapshot meta-data for PFSs containing each
744 listing all available snapshots and their notes.
745 If no arguments are specified snapshots for the PFS containing the
746 current directory are listed.
747 This is the definitive list of snapshots for the file system.
749 .It Cm prune Ar softlink-dir
750 Prune the file system based on previously created snapshot softlinks.
751 Pruning is the act of deleting file system history.
754 command will delete file system history such that
755 the file system state is retained for the given snapshots,
756 and all history after the latest snapshot.
757 By setting the per PFS parameter
759 history is guaranteed to be saved at least this time interval.
760 All other history is deleted.
762 The target directory is expected to contain softlinks pointing to
763 snapshots of the file systems you wish to retain.
764 The directory is scanned non-recursively and the mount points and
765 transaction ids stored in the softlinks are extracted and sorted.
766 The file system is then explicitly pruned according to what is found.
767 Cleaning out portions of the file system is as simple as removing a
768 snapshot softlink and then running the
772 As a safety measure pruning only occurs if one or more softlinks are found
775 snapshot id extension.
776 Currently the scanned softlink directory must contain softlinks pointing
780 The softlinks may specify absolute or relative paths.
781 Softlinks must use 20-character
783 transaction ids, as might be returned from
784 .Nm Cm synctid Ar filesystem .
786 Pruning is a per PFS operation, so a
788 file system and each PFS in it have to be pruned separately.
790 Note that pruning a file system may not immediately free-up space,
791 though typically some space will be freed if a large number of records are
793 The file system must be reblocked to completely recover all available space.
795 Example, lets say your that you didn't set
797 and snapshot directory contains the following links:
798 .Bd -literal -offset indent
799 lrwxr-xr-x 1 root wheel 29 May 31 17:57 snap1 ->
800 /usr/obj/@@0x10d2cd05b7270d16
802 lrwxr-xr-x 1 root wheel 29 May 31 17:58 snap2 ->
803 /usr/obj/@@0x10d2cd13f3fde98f
805 lrwxr-xr-x 1 root wheel 29 May 31 17:59 snap3 ->
806 /usr/obj/@@0x10d2cd222adee364
809 If you were to run the
811 command on this directory, then the
814 mount will be pruned to retain the above three snapshots.
815 In addition, history for modifications made to the file system older than
816 the oldest snapshot will be destroyed and history for potentially fine-grained
817 modifications made to the file system more recently than the most recent
818 snapshot will be retained.
820 If you then delete the
822 softlink and rerun the
825 history for modifications pertaining to that snapshot would be destroyed.
829 file system versions 3+ this command also scans the snapshots stored
830 in the file system meta-data and includes them in the prune.
831 .\" ==== prune-everything ====
832 .It Cm prune-everything Ar filesystem
833 This command will remove all historical records from the file system.
834 This directive is not normally used on a production system.
836 This command does not remove snapshot softlinks but will delete all
837 snapshots recorded in file system meta-data (for file system version 3+).
838 The user is responsible for deleting any softlinks.
840 Pruning is a per PFS operation, so a
842 file system and each PFS in it have to be pruned separately.
843 .\" ==== rebalance ====
844 .It Cm rebalance Ar filesystem Op Ar saturation_percentage
845 This command will rebalance the B-Tree, nodes with small number of
846 elements will be combined and element counts will be smoothed out
849 The saturation percentage is between 50% and 100%.
850 The default is 75% (the
852 suffix is not needed).
854 Rebalancing is a per PFS operation, so a
856 file system and each PFS in it have to be rebalanced separately.
858 .It Cm dedup Ar filesystem
861 Perform offline (post-process) deduplication. Deduplication occurs at
862 the block level, currently only data blocks of the same size can be
863 deduped, metadata blocks can not. The hash function used for comparing
864 data blocks is CRC-32 (CRCs are computed anyways as part of
866 data integrity features, so there's no additional overhead). Since CRC
867 is a weak hash function a byte-by-byte comparison is done before actual
868 deduping. In case of a CRC collision (two data blocks have the same CRC
869 but different contents) the checksum is upgraded to SHA-256.
873 reblocker may partially blow up (re-expand) dedup (reblocker's normal
874 operation is to reallocate every record, so it's possible for deduped
875 blocks to be re-expanded back).
877 Deduplication is a per PFS operation, so a
879 file system and each PFS in it have to be deduped separately. This also
880 means that if you have duplicated data in two different PFSs that data
881 won't be deduped, however the addition of such feature is planned.
882 .\" ==== dedup-simulate ====
883 .It Cm dedup-simulate Ar filesystem
886 Shows potential space savings (simulated dedup ratio) one can get after
889 command. If the estimated dedup ratio is greater than 1.00 you will see
890 dedup space savings. Remember that this is an estimated number, in
891 practice real dedup ratio will be slightly smaller because of
893 bigblock underflows, B-Tree locking issues and other factors.
894 .\" ==== reblock* ====
895 .It Cm reblock Ar filesystem Op Ar fill_percentage
896 .It Cm reblock-btree Ar filesystem Op Ar fill_percentage
897 .It Cm reblock-inodes Ar filesystem Op Ar fill_percentage
898 .It Cm reblock-dirs Ar filesystem Op Ar fill_percentage
899 .It Cm reblock-data Ar filesystem Op Ar fill_percentage
900 Attempt to defragment and free space for reuse by reblocking a live
903 Big-blocks cannot be reused by
905 until they are completely free.
906 This command also has the effect of reordering all elements, effectively
907 defragmenting the file system.
909 The default fill percentage is 100% and will cause the file system to be
910 completely defragmented.
911 All specified element types will be reallocated and rewritten.
912 If you wish to quickly free up space instead try specifying
913 a smaller fill percentage, such as 90% or 80% (the
915 suffix is not needed).
917 Since this command may rewrite the entire contents of the disk it is
918 best to do it incrementally from a
924 options to limit the run time.
925 The file system would thus be defragmented over long period of time.
927 It is recommended that separate invocations be used for each data type.
928 B-Tree nodes, inodes, and directories are typically the most important
929 elements needing defragmentation.
930 Data can be defragmented over a longer period of time.
932 Reblocking is a per PFS operation, so a
934 file system and each PFS in it have to be reblocked separately.
935 .\" ==== pfs-status ====
936 .It Cm pfs-status Ar dirpath ...
937 Retrieve the mirroring configuration parameters for the specified
939 file systems or pseudo-filesystems (PFS's).
940 .\" ==== pfs-master ====
941 .It Cm pfs-master Ar dirpath Op Ar options
942 Create a pseudo-filesystem (PFS) inside a
945 Up to 65535 such file systems can be created.
946 Each PFS uses an independent inode numbering space making it suitable
947 for use as a replication source or target.
951 directive creates a PFS that you can read, write, and use as a mirroring
954 It is recommended to use a
956 mount to access a PFS, for more information see
958 .\" ==== pfs-slave ====
959 .It Cm pfs-slave Ar dirpath Op Ar options
960 Create a pseudo-filesystem (PFS) inside a
963 Up to 65535 such file systems can be created.
964 Each PFS uses an independent inode numbering space making it suitable
965 for use as a replication source or target.
969 directive creates a PFS that you can use as a mirroring target.
970 You will not be able to access a slave PFS until you have completed the
971 first mirroring operation with it as the target (its root directory will
972 not exist until then).
974 Access to the pfs-slave via the special softlink, as described in the
979 dynamically modify the snapshot transaction id by returning a dynamic result
984 A PFS can only be truly destroyed with the
987 Removing the softlink will not destroy the underlying PFS.
989 It is recommended to use a
991 mount to access a PFS, for more information see
993 .\" ==== pfs-update ====
994 .It Cm pfs-update Ar dirpath Op Ar options
995 Update the configuration parameters for an existing
997 file system or pseudo-filesystem.
998 Options that may be specified:
999 .Bl -tag -width indent
1000 .It Cm sync-beg-tid= Ns Ar 0x16llx
1001 This is the automatic snapshot access starting transaction id for
1003 This parameter is normally updated automatically by the
1007 It is important to note that accessing a mirroring slave
1008 with a transaction id greater than the last fully synchronized transaction
1009 id can result in an unreliable snapshot since you will be accessing
1010 data that is still undergoing synchronization.
1012 Manually modifying this field is dangerous and can result in a broken mirror.
1013 .It Cm sync-end-tid= Ns Ar 0x16llx
1014 This is the current synchronization point for mirroring slaves.
1015 This parameter is normally updated automatically by the
1019 Manually modifying this field is dangerous and can result in a broken mirror.
1020 .It Cm shared-uuid= Ns Ar uuid
1021 Set the shared UUID for this file system.
1022 All mirrors must have the same shared UUID.
1023 For safety purposes the
1025 directives will refuse to operate on a target with a different shared UUID.
1027 Changing the shared UUID on an existing, non-empty mirroring target,
1028 including an empty but not completely pruned target,
1029 can lead to corruption of the mirroring target.
1030 .It Cm unique-uuid= Ns Ar uuid
1031 Set the unique UUID for this file system.
1032 This UUID should not be used anywhere else,
1033 even on exact copies of the file system.
1034 .It Cm label= Ns Ar string
1035 Set a descriptive label for this file system.
1036 .It Cm snapshots= Ns Ar string
1037 Specify the snapshots directory which
1040 will use to manage this PFS.
1041 .Bl -tag -width indent
1042 .It Nm HAMMER No version 2-
1043 The snapshots directory does not need to be configured for
1044 PFS masters and will default to
1045 .Pa <pfs>/snapshots .
1047 PFS slaves are mirroring slaves so you cannot configure a snapshots
1048 directory on the slave itself to be managed by the slave's machine.
1049 In fact, the slave will likely have a
1051 sub-directory mirrored
1052 from the master, but that directory contains the configuration the master
1053 is using for its copy of the file system, not the configuration that we
1054 want to use for our slave.
1056 It is recommended that
1057 .Pa <fs>/var/slaves/<name>
1058 be configured for a PFS slave, where
1064 is an appropriate label.
1065 .It Nm HAMMER No version 3+
1066 The snapshots directory does not need to be configured for PFS masters or
1068 The snapshots directory defaults to
1069 .Pa /var/hammer/<pfs>
1070 .Pa ( /var/hammer/root
1074 You can control snapshot retention on your slave independent of the master.
1075 .It Cm snapshots-clear
1078 directory path for this PFS.
1079 .It Cm prune-min= Ns Ar N Ns Cm d
1080 .It Cm prune-min= Ns Oo Ar N Ns Cm d/ Oc Ns \
1081 Ar hh Ns Op Cm \&: Ns Ar mm Ns Op Cm \&: Ns Ar ss
1082 Set the minimum fine-grained data retention period.
1084 always retains fine-grained history up to the most recent snapshot.
1085 You can extend the retention period further by specifying a non-zero
1087 Any snapshot softlinks within the retention period are ignored
1088 for the purposes of pruning (the fine grained history is retained).
1089 Number of days, hours, minutes and seconds are given as
1094 Because the transaction id in the snapshot softlink cannot be used
1095 to calculate a timestamp,
1097 uses the earlier of the
1101 field of the softlink to
1102 determine which snapshots fall within the retention period.
1103 Users must be sure to retain one of these two fields when manipulating
1106 .\" ==== pfs-upgrade ====
1107 .It Cm pfs-upgrade Ar dirpath
1108 Upgrade a PFS from slave to master operation.
1109 The PFS will be rolled back to the current end synchronization transaction id
1110 (removing any partial synchronizations), and will then become writable.
1114 currently supports only single masters and using
1115 this command can easily result in file system corruption
1116 if you don't know what you are doing.
1118 This directive will refuse to run if any programs have open descriptors
1119 in the PFS, including programs chdir'd into the PFS.
1120 .\" ==== pfs-downgrade ====
1121 .It Cm pfs-downgrade Ar dirpath
1122 Downgrade a master PFS from master to slave operation.
1123 The PFS becomes read-only and access will be locked to its
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-destroy ====
1129 .It Cm pfs-destroy Ar dirpath
1130 This permanently destroys a PFS.
1132 This directive will refuse to run if any programs have open descriptors
1133 in the PFS, including programs chdir'd into the PFS.
1134 .\" ==== mirror-read ====
1135 .It Cm mirror-read Ar filesystem Op Ar begin-tid
1136 Generate a mirroring stream to stdout.
1137 The stream ends when the transaction id space has been exhausted.
1138 .\" ==== mirror-read-stream ====
1139 .It Cm mirror-read-stream Ar filesystem Op Ar begin-tid
1140 Generate a mirroring stream to stdout.
1141 Upon completion the stream is paused until new data is synced to the
1144 Operation continues until the pipe is broken.
1147 command for more details.
1148 .\" ==== mirror-write ====
1149 .It Cm mirror-write Ar filesystem
1150 Take a mirroring stream on stdin.
1152 This command will fail if the
1154 configuration field for the two file systems do not match.
1157 command for more details.
1159 If the target PFS does not exist this command will ask you whether
1160 you want to create a compatible PFS slave for the target or not.
1161 .\" ==== mirror-dump ====
1167 to dump an ASCII representation of the mirroring stream.
1168 .\" ==== mirror-copy ====
1169 .\".It Cm mirror-copy Ar [[user@]host:]filesystem [[user@]host:]filesystem
1170 .It Cm mirror-copy \
1171 Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem \
1172 Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem
1173 This is a shortcut which pipes a
1178 If a remote host specification is made the program forks a
1184 on the appropriate host.
1185 The source may be a master or slave PFS, and the target must be a slave PFS.
1187 This command also establishes full duplex communication and turns on
1188 the 2-way protocol feature
1190 which automatically negotiates transaction id
1191 ranges without having to use a cyclefile.
1192 If the operation completes successfully the target PFS's
1195 Note that you must re-chdir into the target PFS to see the updated information.
1196 If you do not you will still be in the previous snapshot.
1198 If the target PFS does not exist this command will ask you whether
1199 you want to create a compatible PFS slave for the target or not.
1200 .\" ==== mirror-stream ====
1201 .\".It Cm mirror-stream Ar [[user@]host:]filesystem [[user@]host:]filesystem
1202 .It Cm mirror-stream \
1203 Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem \
1204 Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem
1205 This is a shortcut which pipes a
1206 .Cm mirror-read-stream
1210 This command works similarly to
1212 but does not exit after the initial mirroring completes.
1213 The mirroring operation will resume as changes continue to be made to the
1215 The command is commonly used with
1219 options to keep the mirroring target in sync with the source on a continuing
1222 If the pipe is broken the command will automatically retry after sleeping
1224 The time slept will be 15 seconds plus the time given in the
1228 This command also detects the initial-mirroring case and spends some
1229 time scanning the B-Tree to find good break points, allowing the initial
1230 bulk mirroring operation to be broken down into 100MB pieces.
1231 This means that the user can kill and restart the operation and it will
1232 not have to start from scratch once it has gotten past the first chunk.
1235 option may be used to change the size of pieces and the
1237 option may be used to disable this feature and perform an initial bulk
1239 .\" ==== version ====
1240 .It Cm version Ar filesystem
1241 This command returns the
1243 file system version for the specified
1245 as well as the range of versions supported in the kernel.
1248 option may be used to remove the summary at the end.
1249 .\" ==== version-upgrade ====
1250 .It Cm version-upgrade Ar filesystem Ar version Op Cm force
1251 This command upgrades the
1256 Once upgraded a file system may not be downgraded.
1257 If you wish to upgrade a file system to a version greater or equal to the
1258 work-in-progress version number you must specify the
1261 Use of WIP versions should be relegated to testing and may require wiping
1262 the file system as development progresses, even though the WIP version might
1266 This command operates on the entire
1268 file system and is not a per PFS operation.
1269 All PFS's will be affected.
1270 .Bl -tag -width indent
1273 default version, first
1278 New directory entry layout.
1279 This version is using a new directory hash key.
1282 New snapshot management, using file system meta-data for saving
1283 configuration file and snapshots (transaction ids etc.).
1284 Also default snapshots directory has changed.
1288 New undo/redo/flush, giving HAMMER a much faster sync and fsync.
1291 .Sh PSEUDO-FILESYSTEM (PFS) NOTES
1292 The root of a PFS is not hooked into the primary
1294 file system as a directory.
1297 creates a special softlink called
1299 (exactly 10 characters long) in the primary
1303 then modifies the contents of the softlink as read by
1305 and thus what you see with an
1307 command or if you were to
1310 If the PFS is a master the link reflects the current state of the PFS.
1311 If the PFS is a slave the link reflects the last completed snapshot, and the
1312 contents of the link will change when the next snapshot is completed, and
1317 utility employs numerous safeties to reduce user foot-shooting.
1320 directive requires that the target be configured as a slave and that the
1322 field of the mirroring source and target match.
1323 .Sh UPGRADE INSTRUCTIONS HAMMER V1 TO V2
1324 This upgrade changes the way directory entries are stored.
1325 It is possible to upgrade a V1 file system to V2 in place, but
1326 directories created prior to the upgrade will continue to use
1329 Note that the slave mirroring code in the target kernel had bugs in
1330 V1 which can create an incompatible root directory on the slave.
1333 master created after the upgrade with a
1335 slave created prior to the upgrade.
1337 Any directories created after upgrading will use a new layout.
1338 .Sh UPGRADE INSTRUCTIONS HAMMER V2 TO V3
1339 This upgrade adds meta-data elements to the B-Tree.
1340 It is possible to upgrade a V2 file system to V3 in place.
1341 After issuing the upgrade be sure to run a
1344 to perform post-upgrade tasks.
1346 After making this upgrade running a
1351 directory for each PFS mount into
1352 .Pa /var/hammer/<pfs> .
1355 root mount will migrate
1358 .Pa /var/hammer/root .
1359 Migration occurs only once and only if you have not specified
1360 a snapshots directory in the PFS configuration.
1361 If you have specified a snapshots directory in the PFS configuration no
1362 automatic migration will occur.
1364 For slaves, if you desire, you can migrate your snapshots
1365 config to the new location manually and then clear the
1366 snapshot directory configuration in the slave PFS.
1367 The new snapshots hierarchy is designed to work with
1368 both master and slave PFSs equally well.
1370 In addition, the old config file will be moved to file system meta-data,
1371 editable via the new
1375 The old config file will be deleted.
1376 Migration occurs only once.
1378 The V3 file system has new
1380 directives for creating snapshots.
1381 All snapshot directives, including the original, will create
1382 meta-data entries for the snapshots and the pruning code will
1383 automatically incorporate these entries into its list and
1384 expire them the same way it expires softlinks.
1385 If you by accident blow away your snapshot softlinks you can use the
1387 directive to get a definitive list from the file system meta-data and
1388 regenerate them from that list.
1393 to backup file systems your scripts may be using the
1395 directive to generate transaction ids.
1396 This directive does not create a snapshot.
1397 You will have to modify your scripts to use the
1399 directive to generate the linkbuf for the softlink you create, or
1400 use one of the other
1405 directive will continue to work as expected and in V3 it will also
1406 record the snapshot transaction id in file system meta-data.
1407 You may also want to make use of the new
1409 tag for the meta-data.
1412 If you used to remove snapshot softlinks with
1414 you should probably start using the
1416 directive instead to also remove the related meta-data.
1417 The pruning code scans the meta-data so just removing the
1418 softlink is not sufficient.
1419 .Sh UPGRADE INSTRUCTIONS HAMMER V3 TO V4
1420 This upgrade changes undo/flush, giving faster sync.
1421 It is possible to upgrade a V3 file system to V4 in place.
1422 This upgrade reformats the UNDO FIFO (typically 1GB), so upgrade might take
1423 a minute or two depending.
1425 Version 4 allows the UNDO FIFO to be flushed without also having
1426 to flush the volume header, removing 2 of the 4 disk syncs typically
1429 and removing 1 of the 2 disk syncs typically
1430 required for a flush sequence.
1431 Version 4 also implements the REDO log (see below) which is capable
1432 of fsync()ing with either one disk flush or zero disk flushes.
1433 .Sh FSYNC FLUSH MODES
1435 implements five different fsync flush modes via the
1436 .Va vfs.hammer.fsync_mode
1439 version 4+ file systems.
1443 fsync mode 3 is set by default.
1444 REDO operation and recovery is enabled by default.
1445 .Bl -tag -width indent
1447 Full synchronous fsync semantics without REDO.
1450 will not generate REDOs.
1453 will completely sync
1454 the data and meta-data and double-flush the FIFO, including
1455 issuing two disk synchronization commands.
1456 The data is guaranteed
1457 to be on the media as of when
1460 Needless to say, this is slow.
1462 Relaxed asynchronous fsync semantics without REDO.
1464 This mode works the same as mode 0 except the last disk synchronization
1465 command is not issued.
1466 It is faster than mode 0 but not even remotely
1467 close to the speed you get with mode 2 or mode 3.
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
1472 might not have made it to the media if the storage system crashes at a bad
1476 Full synchronous fsync semantics using REDO.
1477 NOTE: If not running
1478 a HAMMER version 4 filesystem or later mode 0 is silently used.
1481 will generate REDOs in the UNDO/REDO FIFO based on a heuristic.
1482 If this is sufficient to satisfy the
1484 operation the blocks
1485 will be written out and
1487 will wait for the I/Os to complete,
1488 and then followup with a disk sync command to guarantee the data
1489 is on the media before returning.
1490 This is slower than mode 3 and can result in significant disk or
1491 SSDs overheads, though not as bad as mode 0 or mode 1.
1494 Relaxed asynchronous fsync semantics using REDO.
1495 NOTE: If not running
1496 a HAMMER version 4 filesystem or later mode 1 is silently used.
1499 will generate REDOs in the UNDO/REDO FIFO based on a heuristic.
1500 If this is sufficient to satisfy the
1502 operation the blocks
1503 will be written out and
1505 will wait for the I/Os to complete,
1508 issue a disk synchronization command.
1510 Note that there is no chance of meta-data corruption when using this
1511 mode, it simply means that the data you wrote and then
1514 not have made it to the media if the storage system crashes at a bad
1517 This mode is the fastest production fsyncing mode available.
1518 This mode is equivalent to how the UFS fsync in the
1528 This mode is primarily designed
1529 for testing and should not be used on a production system.
1531 .Sh RESTORING FROM A SNAPSHOT BACKUP
1532 You restore a snapshot by copying it over to live, but there is a caveat.
1533 The mtime and atime fields for files accessed via a snapshot is locked
1534 to the ctime in order to keep the snapshot consistent, because neither
1535 mtime nor atime changes roll any history.
1537 In order to avoid unnecessary copying it is recommended that you use
1541 when doing the copyback. Also make sure you traverse the snapshot softlink
1542 by appending a ".", as in "<snapshotpath>/.", and you match up the directory
1547 If the following environment variables exist, they will be used by:
1548 .Bl -tag -width ".Ev EDITOR"
1550 The editor program specified in the variable
1552 will be invoked instead of the default editor, which is
1560 .Bl -tag -width ".It Pa <fs>/var/slaves/<name>" -compact
1561 .It Pa <pfs>/snapshots
1562 default per PFS snapshots directory
1565 .It Pa /var/hammer/<pfs>
1566 default per PFS snapshots directory (not root)
1569 .It Pa /var/hammer/root
1570 default snapshots directory for root directory
1573 .It Pa <snapshots>/config
1580 .It Pa <fs>/var/slaves/<name>
1581 recommended slave PFS snapshots directory
1590 .Xr periodic.conf 5 ,
1591 .Xr mount_hammer 8 ,
1597 utility first appeared in
1600 .An Matthew Dillon Aq dillon@backplane.com
tuxillo's projects / dragonfly.git / blob