FSArchiver is a system tool that allows you to save the contents of a filesystem to a compressed archive file. The filesystem contents can be restored on a device which has a different size and it can be restored on a different filesystem. Unlike tar/dar, FSArchiver also creates the filesystem when it extracts the data to devices. Everything is checksummed in the archive in order to protect the data. If the archive is corrupt, you just lose the current file, not the whole archive. FSArchiver is released under the GPLv2 license. You should read the Quick Start guide [http://www.fsarchiver.org/quickstart/] if you are using FSArchiver for the first time.
The purpose of this project is to provide a safe and flexible filesystem backup/deployment tool. Other open-source filesystems tools such as Partimage already exist. These tools are working at the filesystem block level, so it's not possible to restore the backup to a smaller device, and restoring to a bigger one forces you to resize the filesystem by hand.
The purpose is to have a very flexible program. FSArchiver can extract an archive to a device which is smaller that the original one as long as there is enough space to store the data. It can also restore the data on a different filesystem, so you can use it when you want to convert your filesystem: you can backup an EXT3 filesystem, and restore it as ReiserFS.
FSArchiver works at the file level. It can make an archive of most Linux filesystems (EXT3, ReiserFS, XFS, ...) that the running kernel can mount with read-write support. It will preserve all the standard Unix file attributes (permissions, timestamps, symbolic-links, hard-links, extended-attributes, ...), as long as the kernel has support for them enabled.
There are limitations anyway: FAT filesystem is supported basically for EFI System Partition volumes (UEFI systems) and won't work for bootable Windows volumes. Also, NTFS support is experimental and shouldn't be used in production. FSArchiver won't preserve features which are very specific to a filesystem. For instance, if you create a snapshot in a Btrfs volume, FSArchiver won't know anything about that, and it will just backup the contents seen when you mount the device.
FSArchiver is safe when it makes backups of devices which are not mounted or are mounted read-only. There is an option to force the backup of a read-write mounted volume, but there may be problems with the files that changed during the backup. If you want to backup a device which are in use, the best thing to do is to make an LVM snapshot of it using lvcreate -s, which is part of the LVM userland tools. Unfortunately you can only make snapshots of devices which are LVM Logical Volumes.
FSArchiver is using two levels of checksums to protect your data against corruption. Each block of each file has a 32-bit checksum written in the archive. That way we can identify which block of your file is damaged. Once a file has been restored, the MD5 checksum of the whole file is compared to the original MD5. It's a 128-bit checksum, so it will detect all file corruptions. In case one file is damaged, FSArchiver will restore all the other files from your archive, so you won't lose all your data. It's very different from tar.gz where the whole tar is compressed with gzip. In that case, the data which are written after the corruption are lost. FSArchiver-0.2.3 and newer versions are able to ignore corrupt contents in an archive file, so all the other files will be restored.