Messages in this thread | | | From | "Petrucci, Joseph" <> | Subject | RE: lack of raw disk devices | Date | Tue, 6 Jan 1998 08:16:46 -0600 |
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Wouldn't this solution be just as difficult to implement as Raw devices???
> -----Original Message----- >From: linux kernel account [SMTP:linker@nightshade.z.ml.org] >Sent: Monday, January 05, 1998 8:51 PM >To: pmonta@imedia.com >Cc: jhohertz@golden.net; h.milz@seneca.muc.de; linux-kernel@vger.rutgers.edu >Subject: Re: lack of raw disk devices> >. >On Mon, 5 Jan 1998, Peter Monta wrote:> > >> A raw device doesn't go through the buffer cache. For example, if you >> issue two reads for the same block, a raw device will physically go >> out to disk each time, whereas a buffered device will satisfy the >> second request from the cache. >> >> I've read all of the discussion I can find about this, in linux-kernel >> archives and elsewhere, and while I don't want to beat a dead horse, I >> disagree with those who say raw devices are useless or intrinsically >> bad. Granted, the vast majority of the time a buffered device is the >> right thing. But I have one application in mind that cries out for a >> raw device---it involves moving digital video as fast as possible from >> disk to DRAM (and subsequently out to a PCI bus master). The system >> will never again need to refer to this data, so a buffered device both >> incurs a copying expense (from buffer cache to DRAM buffer) and >> trashes the buffer cache to no purpose. > >They are not bad, however, the implimentation would be sufficently >difficult and cumbersom, to mostly out weigh the benifits.. In the future, >it would be nice if you could adjust the buffercache characteristics on a >device by device basis and potentiall on each group of block reads >(wouldn't it be neat if ext2fs could be told by the app 'this is a mpg >movie dont cache it' while it's accessed, while the rest of the device >would be cached normally).. > >> >> Cheers, >> Peter Monta pmonta@imedia.com >> Imedia Corp.
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