Copyright 2001 by Theodore Ts'o. All Rights Reserved.
This file may be copied under the terms of the GNU Public License.
If image-file is -, then the output of e2image will be sent to standard output, so that the output can be piped to another program, such as gzip (1). (Note that is currently only supported when creating a raw image file using the -r option, since the process of creating a normal image file currently requires random-access access to the file, which can not be done using a pipe. This restriction will hopefully be lifted in a future version of e2image .)
The -r option will create a raw image file instead of a normal image file. A raw image file differs from a normal image file in two ways. First, the filesystem metadata is placed in the proper position so that e2fsck, dumpe2fs, debugfs, etc. can be run directly on the raw image file. In order to minimize the amount of disk space consumed by a raw image file, the file is created as a sparse file. (Beware of copying or compressing/decompressing this file with utilities that don't understand how to create sparse files; the file will become as large as the filesystem itself!) Secondly, the raw image file also includes indirect blocks and data blocks, which the current image file does not have, although this may change in the future.
It is a very good idea to periodically (at boot time and every week or so) to create image files for all of filesystems on a system, as well as saving the partition layout (which can be generated using the using fdisk -l command). Ideally the image file should be stored on some filesystem other that the filesystem whose data it contains, to ensure that its data is accessible in the case where the filesystem has been badly damaged.
To save disk space, e2image creates the image file as a sparse file. Hence, if the image file needs to be copied to another location, it should either be compressed first or copied using the --sparse=always option to GNU version of cp .
The size of an ext2 image file depends primarily on the size of the filesystems and how many inodes are in use. For a typical 10 gigabyte filesystem, with 200,000 inodes in use out of 1.2 million inodes, the image file be approximately 35 megabytes; a 4 gigabyte filesystem with 15,000 inodes in use out of 550,000 inodes will result in a 3 megabyte image file. Image files tend to be quite compressible; an image file taking up 32 megabytes of space on disk will generally compress down to 3 or 4 megabytes.