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From: steve@Watt.COM (Steve Watt)
Date: Wed, 21 Apr 2004 13:37:49 -0700
In-Reply-To: Julian Elischer <julian@elischer.org>
       "Re: how to flush out cache.?" (Apr 21, 13:28)
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To: Julian Elischer <julian@elischer.org>
cc: hackers@freebsd.org
Subject: Re: how to flush out cache.?
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On Apr 21, 13:28, Julian Elischer wrote:
} Subject: Re: how to flush out cache.?
} 
} On Wed, 21 Apr 2004, Steve Watt wrote:
} 
} > In article <Pine.BSF.4.21.0404211219460.31770-100000@InterJet.elischer.org> you write:
} > >
} > >Ok so I have an application where I need to 
} > >reread a file I have just written to ensure that it went to disk
} > >correctly..
} > 
} > What are you hoping to accomplish?  There are probably other ways
} > to solve the larger problem.
} 
} I thought I was being clear..
} I need to remove all the pages from cache so that a reread of the file
} is forced to go to disk.
} and I don't want to go read a 2GB dummy file to force the flush..

No, my question is "what are you trying to accomplish with the
reread", at a higher level than "I want to know it's on disk".  Is
there some reason you have for not trusting the hardware?  Are you
trying to do a database commit protocol?  Debugging the storage
system?

} Someone suggested that I read the file usign 'dump' through the raw
} device..

Even doing that doesn't necessarily mean the bits have made it onto
the rotating media.  There can also be caches in the disk controller,
and/or caches on the drive itself.  If you're trying for a case where
you want to pull the power, unmounting and remounting the filesystem
will get it about as close as you can.

-- 
Steve Watt KD6GGD  PP-ASEL-IA          ICBM: 121W 56' 57.8" / 37N 20' 14.9"
 Internet: steve @ Watt.COM                         Whois: SW32
   Free time?  There's no such thing.  It just comes in varying prices...