cloning a drive [was: war story]

Lennart Sorensen lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys at public.gmane.org
Wed Jul 27 17:21:54 UTC 2011


On Wed, Jul 27, 2011 at 12:53:42PM -0400, D. Hugh Redelmeier wrote:
> 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.

Yes NTFS can do it, although most people don't.  NT 3.5 was Posix
compliant after all.  It was a US government checklist requirement.

-- 
Len Sorensen
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