| Date: Fri, 19 Jul 2002 14:28:42 +0100
| From: Niall O Broin <niall@linux.ie>
|
| I have about 60G of data which I need to copy from one disk
| to another.  However, I'm not sure how I should best copy it.
| The problem is the bulk of the data is images and most of these
| image have two directory entries i.e. there is a hard link to
| each file.  If I copy them using cp -a or my usual favourite of
| find .|cpio -pmd other_dir  it's going to copy each file twice,
| which is not what I want. dump / restore would take care of this
| if the source filesystem wasn't reiserfs  :-(  Any suggestions ?
do your (and my) favourite, it'll be Ok:
1. cpio(1) preserves hard links, i.e., if F1 and F2 are
hard-linked and both are "copied", then the "copies"
are also hard-linked.  this is true of all `cpio's
(and `tar' and any other decent/usable archival tool,
by definition (IMHO)).
2. `cpio -p' (at least `GNU cpio version 2.4.2') will only
read/write (copy) the actual data bytes once.  I _think_
this is true for all `cpio's (not just that GNU version),
but am not certain.
if you use an intermediate archive, e.g.:
cpio -o ... >file;   ...;   cpio -i ... <file
then the actual data bytes are copied into the archive (file)
under each name (e.g., as both F1 and F2).  but GNU `cpio' is
smart about this in pass-through mode (`-p'), copying the data
just once (or so I read the source).
cheers!
-blf-
p.s. assuming this is a one-time operation that you won't repeat
anytime soon (e.g., never; i.e., time isn't a major issue),
and are not using any intermediate media/file (so storage
isn't an issue), then even if `cpio' did read the data twice,
so what? --- as long as, of course, it re-creates the hard
links.  which it will.
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