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?

we are getting data curruptions occasionally and we are trying to track
it down..

if we wait a half hour so the cache is flushed out, teh file sometimes
checksums differently and has bad data in it
but by then the original files have gone away
so we have a tough time recreating the data..

This is also to help us figure out where the problem is...
but since we have seen this several times we'd like to add a "check that
data on disk" option to our application, to help track this down
in the future if it appears to be happenning again.

if it's happenned several times it can happen again.


> 
> } 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...
>