On Mon, 20 May 2002, Brian Jonnes wrote:
> > dump reads on a lower level than tar, and is more sensitive when dumping > > an active file system. Dumps may be rendered useless due to a file > > changing underneath dump. If the system is placed in single user mode > > there should be no problem. If the file system is quiet, there should be > > close to no problems. The 'close' word makes most people switch to tar. > > This does not really make sense. Is "dump" not a standard utility? How do > other Unices work? Dump can't be as simple as "cat /dev/hdX"... what do you > mean by "low-level"? It must have its own file format, surely? Has anyone > looked at the source-code, or should I do that to satisfy my curiosity? dump and restore are the traditional Unix backup programs. They operate on the drive as a collection of disk blocks, below the abstractions of files, links and directories that are created by the filesystems. dump backs up devices, entire filesystems, not parts of a filesystem and not directory trees that span more than one filesystem, using either soft links or mounting one filesystem onto another. dump does not write files and directories to tape, but rather writes the data blocks that are the building blocks of files and directories. tar operates in cooperation with the filesystem; tar writes files and directories to tape. Which backup program is best? dump, says some people. Elizabeth D. Zwicky torture tested lots of backup programs. The clear choice for preserving all your data and all the peculiarities of Unix filesystems is dump, she stated. Elizabeth created filesystems containing a large variety of unusual conditions (and some not so unusual ones) and tested each program by do a backup and restore of that filesystems. The peculiarities included: files with holes, files with holes and a block of nulls, files with funny characters in their names, unreadable and unwriteable files, devices, files that change size during the backup, files that are created/deleted during the backup and more. She presented the results at LISA V in Oct. 1991. I have used dump and was happy until I needed to split a large file system. I then switched to tar. I'm still happy. I can only repeat what has been said earlier: Test them both and choose the one that works for you. -- Ulrik Sandberg
