[Gllug] DD Ext3 Move (was ping)

[t.clarke]

I am rather late into the fray on this,  but for what its worth, my experience
with playing around with partitions (or 'divs' as they are called on SCO) and
copying is (on Unix) as follows and I believe should equally apply to Linux:

1) tar does not, i think, preserve certain kinds of files within in a file
   system properly,  and therefore cpio is preferred for back-up/restore of
   root filesystems.

2) dd works fine in copying a raw filesystem to somewehere else and back again.
   the entire structure of the filesystem is preserved in its identical format.
   it does not seem to matter of the geometry of the destn disk is different
   to the source,  as the filesystem structures (I assume) are all addressed
   as logical blocks relative to the start of the filesystem (leaving the disc
   IO subsystem presumably to translate into phsyical cylinder/head/sector
   addresses).  We regularly dd filesystems off to a tape and then restore to
   another disc.  Mountinmg and using the copy on the other disc works fine.

3) no reason why you should not dd off to a file rather than a raw filesystem,
   providing the destn filesystem can cope with a file big enough.

4) cpio will probably be quicker than dd if the source filesystem is not too
   full,  as the amount of IO will be less, but if the filesystem is fairly
   full and/or contains loads of individual files,  dd is probably quicker and
   you get a straight read across the disc instead of zillions of head movements

5) As an aside I regularly 'push' complete raw filesystems across the internal
   LAN to a 'lukewarm' spare machine.  The copies mount and work fine.  The
   mechanism is a simple program that shoves the whole thing across as a TCP
   stream and is very fast.

Tim
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