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ext2prepare - ext2 filesystem resizing preparation tool
[-d] [-f] [-q] [-v] [-V] device size[b|K|M|G|T]]
The ext2prepare command
modifies an unmounted ext2 filesystem on device so that ext2online(8) program
can later resize the mounted filesystem to be at least as large as size
although the actual maximum size will be some larger multiple of various
filesystem parameters. While ext2prepare must be run on an unmounted filesystem,
device does not have to currently be as large as size. This allows one to
later increase the size of device and do the resize while the filesystem
If the size parameter does not have a modifier, it will be taken
to be in ext2 filesystem blocks (which can be 1k, 2k, or 4k - use dumpe2fs(8)
to find out more information about the current filesystem). The modifiers
b, K, M, G, or T mean the size parameter is given in 512-byte blocks, kilo-,
mega-, giga-, or terabytes respectively.
The ext2prepare program does not
change the size of the actual device. If you wish to enlarge a filesystem,
you must make sure you expand the underlying device first. This can be
done online for Logical Volumes by using lvextend(8) from the LVM package,
or possibly via md or RAID facilities in the hardware if you are not using
partitions. It is not possible to do this by using the fdisk(8) family
of tools to extend a partition while it is mounted (at least the author
has not been able to successfully do this).
Because of the original design
of the ext2 filesystem did not have online resizing in mind, there are
certain limitations to the amount of resizing that can be done while the
filesystem is mounted, if you haven’t done any preparation for the resize.
The default block size for ext2 was 1k blocks until v1.15 of e2fsprogs
(1999), where it changed to 4k blocks for filesystems larger than 512MB.
With no filesystem preparation, it is always possible to resize to the
next 256MB boundary for 1k filesystems, the next 2GB boundary for for 2k
filesystems, and the next 16GB boundary for 4k filesystems. By using ext2prepare
on an unmounted filesystem, it is possible for ext2online(8) to increase
the size of a mounted ext2 filesystem to at least the given size by reserving
blocks for group descriptors within the ext2 filesystem structure. ext2prepare
does this by moving metadata blocks while the filesystem is unmounted,
and then allocating the freed blocks to a reserved inode so that ext2online(8)
can later use these blocks to safely enlarge the filesystem while the filesystem
is in use.
0 Resizing successful
- -d, --debug
- Turn on debugging messages.
- -f, --force
- Force preparation
without first checking the filesystem state.
- -q, --quiet
- Do not print anything
but error messages.
- -v, --verbose
- Turn on normal verbose status messages.
- Print the version number and exit.
The following example shows how to test ext2prepare with a spare
partition. First a filesystem of 32MB is created on the device. The filesystem
is then prepared to grow to a maximum size of 10GB, mounted, and the size
is verified. The filesystem is then extended to fill the device (the default
action when no size is given), and the new size is verified.
- 1 Error in options or command-line parameters.
- 2 Error while preparing filesystem.
ext2prepare /dev/vg0/lvtest 10G
mount -o debug,check=strict /dev/vg0/lvtest /mnt/test
ext2online -d -v /dev/vg0/lvtest
By using the debug and check=strict options to mount, as
well as the -d and -v options to ext2prepare, we will see the user-space status
messages, and the kernel messages will be logged by syslog.
that resizing a mounted filesystem is inherently dangerous and may corrupt
filesystems, although no errors resulting in data loss have ever been reported
to the author. In theory online resizing should work fine with arbitrarily
large filesystems, but it has not yet been tested by the author on a filesystem
larger than 11GB. Use with caution. Backups are always a good idea, because
your disk may fail at any time, you delete files by accident, or your computer
is struck by a meteor.
The ext2prepare program was written by Andreas
Dilger <firstname.lastname@example.org> using the ext2 resizing tools developed by
Lennert Buytenhek <email@example.com>. The ext2online kernel patches are available
as part of the GNU ext2resize package at <http://sourceforge.org/projects/ext2resize/>.
Because ext2prepare uses a reserved inode to store blocks needed for
a future resize (so that they can’t be accidentally used by another program),
e2fsck(8) needs to be slightly modified to understand this new reserved
inode. If an unmodified e2fsck(8) is run on a filesystem that has been changed
with ext2prepare, it will complain about the reserved inode and free all
of the blocks associated with this inode. If this happens, it will not
be possible to resize the filesystem past the default limits given previously.
However, the filesystem itself is not affected in any way by these events.
The ext2resize programs do not work on big-endian machines (Alpha, SPARC,
ext2prepare is (C) Copyright 1999, 2000, 2001 by Andreas
Dilger and may be distributed under the terms of the GNU General Public
dumpe2fs(8) ext2online(8) ext2resize(8) e2fsck(8) lvextend(8)
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