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From: mouse@thunder.mcrcim.mcgill.edu (der Mouse)
Subject: Re: How do you determine what physical device a file in on?
Message-ID: <1991Jun30.225619.8042@thunder.mcrcim.mcgill.edu>
Organization: McGill Research Centre for Intelligent Machines
References: <1991Jun25.174729.11481@StarConn.com>
Date: Sun, 30 Jun 91 22:56:19 GMT
Lines: 29

In article <1991Jun25.174729.11481@StarConn.com>, dror@StarConn.com (Dror Matalon) writes:

> I suspect that there are only machine dependent ways.  Given two
> files x and y. I want to determine if they're on the same PHYSICAL
> devie.

Right you are: it's machine-dependent at best and impossible at worst.
(Suppose it's NFS-mounted from wuarchive.wustl.edu; how do you tell
whether they've got that tree on multiple drives?)

For that matter, either or both of the files may be on more than one
physical device.  As a simple example, consider disk striping, which
causes some pieces of the file to be on one device and other pieces on
others; for another, consider disk mirroring, which causes the file to
be entirely present on multiple devices.

For that matter, how do you define a physical device?  Disk drive?
Disk spindle?  Disk platter?  Disk surface?  Disk track?

Or the file may be on a RAMdisk, which arguably comes close to not
being on any physical device.

Why do you care whether they're on the same physical device?

					der Mouse

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