On Tue, Dec 23, 2003 at 11:42:14AM -0500, Henson, George Mr JMLFDC wrote:
> What are the advantages or disadvantages to using tar instead
> of dump?

(This is partially brief repetition, but also contains new
points.)

In dump's favour:
  - The estimate phase is faster

  - It doesn't change any of the timestamps of files it's backing
    up (tar doesn't change mtime either of course, but can't
    avoid changing either atime or ctime (actually, I recently
    read that Solaris provides a way, if you're root, but I don't
    know whether GNU tar takes advantage of it)

  - You can do interactive restores natively.  (amrecover gives
    you the same functionality, regardless of dump vs. tar, so
    this difference *only* applies if Amanda isn't in the loop at
    restore time, or if you don't have the index files, which
    amrecover requires.)

  - Dump programs are customized to the local file system's
    idiosyncracies.  I'm guessing (but don't know) that this
    means that dump can back up system-dependent metadata that
    tar has no clue about (ACLs, Linux ext2 "chattr" flags,
    FreeBSD's "chflags" variant thereof, and the like)

In tar's favour:
  - You can exclude files

  - You can split a partition into multiple DLE's.  This is
    necessary if you have partitions larger than will fit on a
    single tape, since Amanda can't split a single dump onto
    multiple tapes (not yet anyway; work is in progress,
    hooray!).

  - Dump is reported to be undependable on Linux -- Linus says
    so, anyway.  (He has a thing against dump, so doesn't see
    that as a problem, but IMO it's because Linux has deviated
    from standard UNIX in undesirable ways.  Regardless of blame,
    though, it's an issue to be dealt with.)

  - Backups are portable.  The downside of every dump being
    customized to its file system is that you very likely can't
    restore a dump from platform X using platform Y's "restore".
    I've never tried cross-file-system restores on the same box
    (restoring from a Solaris VXFS dump onto a Solaris ufs
    partition, for example), but I imagine that whether you can
    get away with it depends on the specific combination and the
    specific platform.

--

|  | /\
|-_|/  >   Eric Siegerman, Toronto, Ont.        erics AT telepres DOT com
|  |  /
It must be said that they would have sounded better if the singer
wouldn't throw his fellow band members to the ground and toss the
drum kit around during songs.
        - Patrick Lenneau