ext2online - online (mounted) ext2 filesystem resizer

ext2online [-C fd] [-d] [-q] [-v] [-V] {device|mountpoint} [size[b|K|M|G|T]]

The ext2online tool resizes ext2 file systems while they are mounted and in use by the system. It is OK to resize the filesystem even while programs have open files and are writing into the filesystem. It is only possible to enlarge a mounted filesystem. It is possible to use ext2resize(8) to shrink and enlarge an unmounted filesystem. To be able to use ext2online, you need to have the Online ext2 resize support (CONFIG_EXT2_RESIZE) feature enabled in the kernel (after applying the appropriate patch for the 2.x series of kernels).

The filesystem specified by device (partition, loop device, logical volume, ...) or mountpoint must currently be mounted, and it will be enlarged to fill the device, by default. If the optional size parameter is specified, then this size will be used instead. If the size parameter does not have an optional 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 ext2online program does not change the size of the actual device - only the filesystem. 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 for ease-of-use you can use e2fsadm(8) which combines the LV extension and ext2 filesystem resizing into one step. Alternately, you may be able to use facilities in md or RAID facilities in the hardware, if you are not using a partition table. 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 the ext2prepare(8) program on an unmounted filesystem, it is possible for ext2online to increase the size of a mounted ext2 filesystem to almost any size.

-C fd, --completion=fd Output completion information to file descriptor fd.

-d, --debug

Turn on debugging messages.

-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.

0 Resizing successful

1 Error in command line (options or specified device)

2 Error in specified size

3 Error in pre-resizing (user space) operation

4 Error during the in-kernel resizing operation

5 Error in post-resizing operation (update of metadata backups)

The following example shows how to test ext2online with a spare partition. First a filesystem of 32MB is created on the device, 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.

dd if=/dev/zero of=/tmp/file bs=1k count=64k

mke2fs -F -f 32768 /tmp/file

mkdir /tmp/test

mount -o loop,debug,check=strict /tmp/file /tmp/test

df /mnt/test

ext2online -d -v /tmp/file

df /tmp/test

By using the debug and check=strict options to mount, as well as the -d and -v flags to ext2online, we will see the user-space status messages, and the kernel messages will be logged by syslog.

Note 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 ext2online 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/>.

There is a limit imposed on a single filesystem resize due to the fact that ext2online does not use triple-indirect blocks for the resize inode. This should not affect most users of ext2online, as the limit is about 60GB larger than the current filesystem size for 1k block filesystems. The ext2resize programs do not work on big-endian machines (Alpha, SPARC, PPC, etc).

ext2online is (C) Copyright 1999, 2000, 2001 by Andreas Dilger and may be distributed under the terms of the GNU General Public License.

dumpe2fs(8) ext2prepare(8) ext2resize(8) e2fsadm(8) e2fsck(8) lvextend(8)