cloning a drive [was: war story]

[D. Hugh Redelmeier]

| From: James Knott <james.knott-bJEeYj9oJeDQT0dZR+AlfA at public.gmane.org>

| I thought hard links were deprecated.

By whom?  Perhaps someone who doesn't understand UNIX.

Hard links were one of the great features since the beginning of UNIX.

Symbolic links are a hacky but useful invention of the BSD folks.  I
avoid them when possible.

They were not in 7th Edition UNIX.  I imagine that they were in 10th
Edition.  I think they got added in System V, but I don't remember
which release (certainly by 5.4).

What's bad about symlinks?

- you need two sets of operations on them: the ones that actually deal
  with the symlink, and ones that see through them to the referenced
  file.  Think ls -L.  So this one feature multiplied the complexity
  of the system.

- symlinks can be dangling: the name exists but it references nothing.
  New odd condition.  New error handling paths needed.

- symlinks can create loops in the filesystem.  Not something possible
  before.  So a tree traversal of a filesystem needs to guard against
  that.

- symbolic links are affected by the system in which they are
  interpreted.  symlinks mixed with NFS can be very confusing.

- there are absolute and releative symlinks.  I don't actually have an
  accurate model of how to manipulate them, so I guess most people
  don't.

On the good side, you can symlink to a directory, not something you
are supposed to do with hard links.

Neither kind of link can live in a Microsoft filesystem as far as I
know.  Perhaps NTFS.
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