Subject: Re: Removing GNU tar and GNU cpio from src?
To: None <firstname.lastname@example.org (NetBSD Userlevel Technical Discussion\>
From: Robert Elz <kre@munnari.OZ.AU>
Date: 01/27/2003 10:08:39
Date: Sun, 26 Jan 2003 21:38:14 -0500 (EST)
From: "Greg A. Woods" <email@example.com>
I have no idea why I am bothering, but ...
| Of course personally I wouldn't ever use anything like 'tar' or 'cpio'
| or 'pax', etc. to back up filesystems
I actually (up to this second) used to think this too. Now I have to
go and work out what has been wrong with my thinking, clearly there
has to be something...
| On NetBSD Amanda does just fine with proper 'dump' backups which of
| course face none of these silly issues because 'dump' is a proper backup
Ho ho ho...
Dump silently ignores changes to files that are made while it was running,
which is your definition of a buggy program.
[Odd definition incidentally, most people treat as bugs places where the
program does not act as documented, not where it does not do what Greg
Woods thinks it should do.]
And, as der Mouse said, this is one area where dump is "worse" than
tar, as dump collects all the file sizes as it starts, and then reads
the files (to that size) later, whereas tar [pax] does size & file read
closer together (like very closely together). The opportunity for
file changes with dump is *MUCH* greater (in olden times, dumps used
to happen to multiple 9 track tapes - which needed operator attention
to change - it could easily be many hours between when dump discovered
the size of a file, and eventually wrote exactly that many bytes to
the tape (regardless of what the file is now like).
Of course dump is still orders of magnitude better than tar for filesystem
backups, for all kinds of other reasons. Or I used to believe that until
I just discovered that is your opinion, so know I know I must be worng.