nilfs

Langue: en

Autres versions - même langue

Version: May 2008 (ubuntu - 08/07/09)

Section: 8 (Commandes administrateur)

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  SKT   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  SKT   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.

SKETCH

NILFS2 provides an extended function to associate user-defined data of arbitrary format with checkpoints. This data is called `sketch', and is tagged to a checkpoint by writing its content in a virtual file .sketch before creating the checkpoint. The .sketch file behaves as a regular file except it gets truncated at the instant of the checkpoint creation. It is created by mkfs.nilfs2(8) and is located directly below the top directory of the NILFS2 file system.

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/