Re: Confused about RAW devices ...

Matthew Wilcox (Matthew.Wilcox@genedata.com)
Mon, 18 Oct 1999 20:28:32 +0200


On Mon, Oct 18, 1999 at 05:47:03PM +0200, Dr. Michael Weller wrote:
> Well, you just wrote down the difference. Now, linux (apparently this is
> going to change) has no difference between raw and non raw devices. A more
> classical Unix has block and char devices (the first can only write blocks
> of data, often in a random seek manner, the latter are more like streams
> of data).

Sorry, you're confused about this. The point of raw devices is so that
the application can KNOW that the data has got to the device and that
another system reading from the same device will read the data which it
just wrote. This is exactly what is needed for multiple-server database
applications. Think how bad it would be for your database to write a
block to the shared disc, and then have a different machine access the
stale data which happens to be in its buffer cache.

-- 
Matthew Wilcox <willy@bofh.ai>
"Windows and MacOS are products, contrived by engineers in the service of
specific companies. Unix, by contrast, is not so much a product as it is a
painstakingly compiled oral history of the hacker subculture." - N Stephenson

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