how to flush out cache.?

[Julian Elischer]

On Wed, 21 Apr 2004, Steve Watt wrote:

> 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 at 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.

The disk caches are small enough.. we are talking about multi gigabyte
files getting a few blocks bad somewhere in the middle.
(and yes the machines have enough RAM to cache the files).



> 
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> Steve Watt KD6GGD  PP-ASEL-IA          ICBM: 121W 56' 57.8" / 37N 20' 14.9"
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