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From: seifert@sun1.ruf.uni-freiburg.de (Ulrich Seifert)
Newsgroups: comp.os.os2.misc
Subject: Re: HPFS ... (corrected)
Keywords: HPFS cache UPS
Message-ID: <1990Sep15.161438.15123@sun1.ruf.uni-freiburg.de>
Date: 15 Sep 90 16:14:38 GMT
References: <1990Sep6.141036.11041@sun1.ruf.uni-freiburg.de> <57439@microsoft.UUCP> <1990Sep15.154653.14659@sun1.ruf.uni-freiburg.de>
Distribution: comp
Organization: Rechenzentrum der Universitaet Freiburg, Deutschland
Lines: 46

*** CORRECTED VERSION ***
*** SORRY, LOOKS LIKE MY EDITOR DIDN'T LIKE TO SAVE THIS STUFF ***

gordonl@microsoft.UUCP (Gordon LETWIN) writes:

>This HPFS can be configured to do write behinds; I think that may be the
>default.  This delays writes until the disk goes idle for a couple of
>seconds or until the data gets too old (risky to leave unwritten for
>too long a period of time) or until the cache gets too dirty.  The
>performance effect of this is threefold: ...

Gordon,
thank you very much for your explanations. Although I haven't seen benchmark
results for the performance of the cache system yet the technical part
sounds very good.

Maybe this is the right place to post a related question.
Let us assume we have a power failure. Well, probably everybody thinks the 
damage arising from programs dieing unknowingly in the machine will b much
bigger than everything what happens in the cache. Maybe, but if we are dng
transaction processing we should be sure that the data safely arrive on the 
disk after a commit.
I do *NOT* want to say that all caching with write behinds is nonsense.
But maybe it is not really enough. I think there are many possible situations
where an application should be notified that there is a problem with the power
supply. Of course, I assume that the computer is equipped with an UPS
(otherwise one shouldn't complain). Most of the UPSs give a kind of warning
signal if anything is wrong.
I think it would be a great idea for OS/2 to set up a watchdog kind of 
interface to the UPS and broadcast a *standard* message or warning to every
active application (for example to the PM applications to begin with).
The file subsystem could immediately save the cache and switch to a
no-write-behind mode until the UPS signals that everything is o.k. again.
(And OS/2 could send another standard message to the applications)
The applications could write a kind of restart file for the case
that the power doesn't stabelizes any more or ignore the message. The user 
could go and check the status of his coffee machine instead of hurrying from
one machine to the next and shutting everything down in the correct order.

Wouldn't that be fantastic (and maybe one argument more to give OS/2 a try?).

What do you think out there, maybe we can convince IBM/Microsoft that such a
thing is a must-have for a modern operating system.

Ulf