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To: Irish Linux Users Group <ilug@linux.ie>
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Subject: Re: [ILUG] How to copy some files
In-Reply-To: Message from Niall O Broin <niall@linux.ie> of
    "Fri, 19 Jul 2002 14:28:42 BST."
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Date: Fri, 19 Jul 2002 15:00:12 +0100
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  | 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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