xref: /dflybsd-src/share/man/man5/hammer.5 (revision 5025869ba48632a0fabd65bbaf8ddb98a521a3f5)

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.\" $DragonFly: src/share/man/man5/hammer.5,v 1.1 2008/07/16 12:45:13 swildner Exp $
.\"
.Dd July 16, 2008
.Os
.Dt HAMMER 5
.Sh NAME
.Nm HAMMER
.Nd HAMMER file system
.Sh SYNOPSIS
.Cd options HAMMER
.Pp
In
.Xr fstab 5 :
.Bd -literal
# single volume
#
/dev/disk0a	/mnt hammer rw 2 0

# multi volume
#
/dev/disk0a:/dev/disk1a:/dev/disk2a	/mnt hammer rw 2 0
.Ed
.Sh DESCRIPTION
The
.Nm
file system provides facilities to store file system data onto a disk device
and is intended to replace UFS as the default file system for
.Dx .
Among its features are fine grained history retention, file systems spanning
multiple volumes, mirroring capability, and pseudo file systems.
.Pp
.Nm
file systems are constructed with
.Xr newfs_hammer 8
and mounted with
.Xr mount_hammer 8 .
All other functions related to managing a
.Nm
file system are provided by the
.Xr hammer 8
and
.Xr undo 1
utilities.
.Pp
.Em NOTE:
It is recommended that a nightly
.Xr cron 8
job be set up to reblock each
.Nm
file system over a longer period of time (using the
.Fl c
and
.Fl t
options of the
.Xr hammer 8
utility), for example up to 5 minutes every night.
.Ss Transaction IDs
The
.Nm
file system uses 64 bit, hexadecimal transaction IDs to refer to historical
file or directory data.
An ID has the format
.Li 0x%016llx ,
such as
.Li 0x00000001061a8ba6 .
.Ss History & Pruning
History metadata on the media is updated with every sync operation.
Prior versions of files or directories are accessible by appending
.Li @@
and a transaction ID to the name.
Pruning a
.Nm
file system will free all unused historical records.
.Ss Snapshots
A snapshot can be taken by creating a symbolic link to a specific
version of a file or directory.
Snapshots created this way will be retained across subsequent prune
operations.
Removing the symbolic link enables the file system to reclaim the space
again.
.\".Ss Mirroring
.\".Ss Pseudo File Systems
.\".Sh EXAMPLES
.Sh SEE ALSO
.Xr undo 1 ,
.Xr hammer 8 ,
.Xr mount_hammer 8 ,
.Xr newfs_hammer 8
.Rs
.%A Matthew Dillon
.%D June 2008
.%T "The HAMMER Filesystem"
.Re
.Sh HISTORY
The
.Nm
file system first appeared in
.Dx 1.11 .
.Sh AUTHORS
.An -nosplit
The
.Nm
file system was designed and implemented by
.An Matthew Dillon Aq dillon@backplane.com .
This manual page was written by
.An Sascha Wildner .