[TUHS] dump(8) compatibility

[M. Warner Losh]

In message: <20100215011914.GZ62998 at dereel.lemis.com>
            "Greg 'groggy' Lehey" <grog at lemis.com> writes:
: On Thursday, 28 January 2010 at 15:27:11 -0500, Brad Spencer wrote:
: >
: >    On Thursday, 21 January 2010 at 12:44:49 -0800, Corey Lindsly wrote:
: >>
: >>> Sure. I know.  Big SATA drives are cheap over here as well, like
: >>> 1.5T for 110 EURO or somesuch. I just happen to own a LTO3 and
: >>> enough tapes already, so the economics are not the issue. Just need
: >>> to have a proper piece of open source backup software that runs on
: >>> FreeBSD.
: >>
: >> And what, precisely, is the problem with using dump?
: >> It will span multiple tapes.
: >
: >    dump is non-portable.  In general, you can only restore to the same
: >    kind of system as you write to.
: >
: > Not entirely true...  dump and restore in NetBSD seems to be portable
: > among NetBSD systems at least.
: >
: > I don't know how far this goes, if it is just NetBSD, or something
: > inherent to all 4.4BSD derived systems.
: 
: I've just tried to list a FreeBSD 7.2 dump on NetBSD 5.0.1:
: 
:   Extract directories from tape
:   Mangled directory: reclen less than DIRSIZ (12 < 16)
:   (many repetitions)
:   Mangled directory: reclen less than DIRSIZ (12 < 16)
:   . is not on the tape
:   Root directory is not on tape
:   abort? [yn] y
: 
: Interestingly, FreeBSD restore can understand the NetBSD dump.  But
: it's not even backwards compatible between major releases of FreeBSD
: even, so this might be the same issue as with FreeBSD.  Either way, I
: don't think it's a good idea to count on it for NetBSD in the future.

Actually, dump *IS* compatible between major releases of FreeBSD.  The
problem is that dump tapes from FreeBSD 1.x and 2.x (and 4.3BSD,
4.4BSD and early SunOS) are no longer restoreable because the code
that restored the old-style ufs1 layout was removed somewhere around
FreeBSD 4.x or 5.x.

It used to be the case that dump was completely interchangeable
between the different BSDs, but software drift has rendered that not
the case anymore.

Warner
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