Originally posted by: SystemAdmin
> Sorry for my REALLY stupid question.
The only stupid question, is the one not asked.
I believe the concept you are missing is that
which distinguishes between "logical", "physical",
and "virtual".
"physical" is the attribute of that which has
meaningful existance beyond its information.
The box of platters, drives, etc. that you
manually insert in a bay may be a "physical" disk.
"logical" is the attribute of that which can
be addressed as a functionally-defined entity. Each
partition on a "physical" disk may be mounted
as a "logical" disk, functionally indistiguishable
from any other "logical" disk.
"virtual" is the attribute of that which has
"logical" existance, but no meaningful "physical"
existance. A file can be mounted as a "logical"
disk with the loopback driver. Since the file
has no meaningful "physical" existance (Its
existance depends on interpretation of
information.), the mounted file is a "virtual"
disk.
To unix, "everything is a file". A file that can
be used as <something> is a "logical" <something>.
A file that has a one-to-one existance relation with
a tangible <something> is a "physical" <something>.
A file that is a "logical" <something> but that has
no existance without processing is a "virtual"
<something>. Terminals, disks, and printers, are
common examples of <something>s.
The precise categorization of <something> as
"physical", "virtual", or "logical" depends
on your intended use, so in theory, a "logical"
<something> can be all/many/part of "virtual"
<something-else> and all/many/part of "physical"
<something-else-again>. In practice, good
administration policies minimize maintenance
costs by aligning the "virtual" boundaries
between <something>s with the "physical" bounadaries
between <something-else>s, and the "logical"
boundaries between <something-else-again>s.
Consequently, there is seldom entanglement
(which would require attention to extra <something>s
when one <something> must be maintained).
Hopefully helpful,