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From: ronc@fai.UUCP (Ronald O. Christian)
Newsgroups: net.followup
Subject: Re: FYI: VM systems on the net
Message-ID: <281@fai.UUCP>
Date: Tue, 29-Jul-86 11:32:53 EDT
Article-I.D.: fai.281
Posted: Tue Jul 29 11:32:53 1986
Date-Received: Sat, 2-Aug-86 01:07:02 EDT
References: <455@valid.UUCP> <653@glasgow.glasgow.UUCP> <494@sunybcs.UUCP> <503@valid.UUCP>
Reply-To: ronc@fai.UUCP (Ronald O. Christian)
Organization: Fujitsu America, Inc.
Lines: 32

In article <503@valid.UUCP> gelfand@valid.UUCP (Brooks Gelfand) writes:
>No operating system, by itself, can imporve hardware reliability -
>[..] When the
>hardware crashes you will loose work in progress - the files in core.
>However, you should not have lost any files on disk unless you were 
>writing to them at the time of the crash. Or did you perhaps have a
>disk head crash?
>
>Brooks Gelfand

Not necessarily.  Depends, for instance, on how often the disk is
updated with directory information.  One of the first things OS
engineers discover is that keeping directory info in ram decreases
overhead, speeds things up.  A CPU crash, not a head crash, then
causes loss of data because the directory (superblock, in Unix terminology)
has old information.  How well the OS can recover from this is a
good measure of robustness.  Some do pretty badly.

Besides, I don't think that was the Col.'s point.  I'm not sure how
virtual machines are implemented, but it occurs to me that there is
probably even more possibility of losing files (whole environments?)
if the hardware (on which several virtual machines exist) gets sick.


				Ron
-- 
--
		Ronald O. Christian (Fujitsu America Inc., San Jose, Calif.)
		seismo!amdahl!fai!ronc  -or-   ihnp4!pesnta!fai!ronc

Oliver's law of assumed responsibility:
	"If you are seen fixing it, you will be blamed for breaking it."