ext2prepare(8)

NAME

ext2prepare - ext2 filesystem resizing preparation tool

SYNOPSIS

ext2prepare   [-d]   [-f]   [-q]    [-v]    [-V]    device
size[b|K|M|G|T]]

DESCRIPTION

The ext2prepare command modifies an unmounted ext2

filesystem on device so that ext2online(8) program can later re

size the mounted filesystem to be at least as large as size al

though 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 is mounted.

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 param

eter is given in 512-byte blocks, kilo-, mega-, giga-, or ter

abytes 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 re

serving 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.

OPTIONS

-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.

-V, --version

Print the version number and exit.

RETURN VALUES

0 Resizing successful

1 Error in options or command-line parameters.

2 Error while preparing filesystem.

EXAMPLES

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.

mke2fs /dev/vg0/lvtest 32768
ext2prepare /dev/vg0/lvtest 10G
mkdir /mnt/test
mount -o debug,check=strict /dev/vg0/lvtest /mnt/test
df /mnt/test
ext2online -d -v /dev/vg0/lvtest
df /mnt/test

By using the debug and check=strict options to mount, as

well as the -d and -v options to ext2prepare, we will see the us

er-space status messages, and the kernel messages will be logged

by syslog.

WARNING

Note that resizing a mounted filesystem is inherently dan

gerous 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 filesys

tems, but it has not yet been tested by the author on a filesys

tem 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.

AUTHOR

The ext2prepare program was written by Andreas Dilger

<adilger@clusterfs.com> using the ext2 resizing tools developed

by Lennert Buytenhek <buytenh@gnu.org>. The ext2online kernel

patches are available as part of the GNU ext2resize package at

<http://sourceforge.org/projects/ext2resize/>.

BUGS

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, PPC, etc).

COPYRIGHT

ext2prepare is (C) Copyright 1999, 2000, 2001 by Andreas

Dilger and may be distributed under the terms of the GNU General

Public License.

SEE ALSO

dumpe2fs(8) ext2online(8) ext2resize(8) e2fsck(8)

lvextend(8)

ext2prepare v1.1.18 July 2002

EXT2PREPARE(8)