Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!bfmny0!tneff
From: tneff@bfmny0.UUCP (Tom Neff)
Newsgroups: comp.sys.att
Subject: Re: 6386 shutdown: I CAN'T BELIEVE at&t was really this stupid!
Message-ID: <14402@bfmny0.UUCP>
Date: 16 Jun 89 15:11:24 GMT
References: <483@oglvee.UUCP> <14401@bfmny0.UUCP> <14506@watdragon.waterloo.edu>
Reply-To: tneff@bfmny0.UUCP (Tom Neff)
Organization: ^
Lines: 32

In article <14506@watdragon.waterloo.edu> hjespersen@trillium.waterloo.edu (Hans Jespersen) writes:
>In article <14401@bfmny0.UUCP> tneff@bfmny0.UUCP (Tom Neff) writes:
>>To minimize the risk from power hits and crashes, I add a root cron job
>>that performs a 'sync ; sync' every 10 minutes.  I have not been reliably
>                  ^^^^^^^^^^^  
		I wrote it this way to conserve space;
		actually they're on separate lines of
		a shell script.

>Why do people always do this? Running sync twice does nothing that
>running sync once wouldn't do. 

I experimented with this fairly extensively when this installation was born.
Running 'sync' once, waiting for the hard disk light to go out and then
punching the button nearly always lost some data on the FS check.  Running
it twice never did.

I might add that regardless of the underlying reasons, it CANNOT hurt.

>				Remember that 'sync' does NOT guarantee
>that all delayed writes are actually written out to disk. It mearly
>guarantees that they are in the queue to be written as soon as possible.

That's good enough for the purpose described above.  If you are doing it
by hand preparatory to an emergency powerdown, you should wait until the
disk accesses are visibly done.

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Tom Neff				UUCP:     ...!uunet!bfmny0!tneff
    "Truisms aren't everything."	Internet: tneff@bfmny0.UU.NET