NAME
NILFS - the new implementation of a log-structured file system
SYNOPSIS
Overview of the NILFS file system and the related tools.
DESCRIPTION
NILFS is a log-structured file system developed for Linux. NILFS
provides versioning capability of an entire file system and continuous
snapshotting that allows users to restore files mistakenly overwritten
or destroyed a while ago.
The current major version of NILFS is version 2, which is referred to
as NILFS2. NILFS2 is equipped with an online garbage collector (also
called cleaner) that reclaims disk space in the background with keeping
multiple snapshots.
When data is written or any change is made to a NILFS2 file system, it
automatically creates a checkpoint. A checkpoint represents a
consistent state of the NILFS2 file system of a certain instant. It
becomes mountable after being changed into a snapshot. A snapshot is
the checkpoint marked not to be deleted by the cleaner. NILFS2 creates
a number of checkpoints at regular intervals (unless there is no
change) or with synchronous writings. There is no practical limit on
the number of checkpoints and snapshots.
The following tools are available to manage the checkpoint and the
snapshot:
lscp lists checkpoints or snapshots
mkcp makes a checkpoint or a snapshot
chcp changes an existing checkpoint to a snapshot or vice versa
rmcp invalidates specified checkpoint(s)
These tools give the versioning capability to NILFS2; a user can select
significant versions among continuously created checkpoints and can
change them to snapshots to be preserved for long periods.
Every checkpoint except for the snapshot will become unprotected from
the cleaner after a given period of time. This period is controlled by
the protection_period parameter defined in the
/etc/nilfs_cleanerd.conf(5) file.
MOUNT OPTIONS
Refer to the mount.nilfs2(8).
EXAMPLES
mkfs -t nilfs2 /dev/sdb1
creates a NILFS2 file system on a block device ‘/dev/sdb1’.
mount -t nilfs2 /dev/sdb1 /nilfs
mounts the NILFS2 file system on a mount point ‘/nilfs’ like an
ordinary POSIX file system. This will invoke a cleaner process
nilfs_cleanerd(8) through an external mount program (i.e.
mount.nilfs2(8)).
lscp lists checkpoints created in the file system as follows:
CNO DATE TIME MODE FLG NBLKINC ICNT
1 2008-05-08 14:45:49 cp - 11 3
2 2008-05-08 14:50:22 cp - 200523 81
3 2008-05-08 20:40:34 cp - 136 61
4 2008-05-08 20:41:20 cp - 187666 1604
5 2008-05-08 20:41:42 cp - 51 1634
...
chcp ss 2
changes the checkpoint whose checkpoint-number is two to a
snapshot. Then the checkpoint list will become as follows:
CNO DATE TIME MODE FLG NBLKINC ICNT
1 2008-05-08 14:45:49 cp - 11 3
2 2008-05-08 14:50:22 ss - 200523 81
3 2008-05-08 20:40:34 cp - 136 61
4 2008-05-08 20:41:20 cp - 187666 1604
5 2008-05-08 20:41:42 cp - 51 1634
...
mount -t nilfs2 -r -o cp=2 /dev/sdb1 /snapshot
mounts the snapshot on another directory ‘/snapshot’ as a read-
only file system. Here the snapshot mount requires at least two
options, a read-only option (-r or -o ro) and the cp option (-o
cp=checkpoint-number). Note that a read/write mount and one or
more snapshots are mountable independently, so the online backup
is possible through the snapshot mounts.
# mount -t nilfs2
/dev/sdb1 on /nilfs type nilfs2 (rw,gcpid=13296)
/dev/sdb1 on /snapshot type nilfs2 (ro,cp=2)
umount /nilfs
unmounts the NILFS2 file system mounted on ‘/nilfs’ and will
shutdown the nilfs_cleanerd(8) through an external umount
program (umount.nilfs2(8)) for the read/write mount.
AUTHORS
NILFS2 was developed by NILFS development team <nilfs@osrg.net>.
SEE ALSO
mkfs.nilfs2(8), mount.nilfs2(8), umount.nilfs2(8), nilfs_cleanerd(8),
nilfs_cleanerd.conf(5), lscp(1), mkcp(8), chcp(8), rmcp(8), lssu(1),
dumpseg(8)
http://www.nilfs.org/