tar fs copy

[Guy Harris]

> Pipes use an inode on the root file system.

Not in systems since V7; in V7, a "pipe device" was added, so that you can
put pipes on other file systems if you want.

Other systems, like 4.2BSD, use mechanisms other than pseudo-files to buffer
pipe data.

> They are limited to 5120 bytes on System V, and 4096 on some other systems,
> by code in the kernel.

To clarify - this is not a limit on the total amount of data which can be
poured down a pipe (which seems to be what the previous poster was worried
about, since they were using something like two piped-together "tar"s to
copy a huge file system).  This is a limit on how much data can be buffered
in a pipe before the writer is blocked.  Chances are slim (if not
nil) that you won't be able to copy a big file system using piped-together
"tar"s because of the pipe filling up the file system (unless, of course,
you're moving data to the file system on which the pipes exist).

	Guy Harris