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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