Using the raw disk partition

[martin.zam]

: I've read of databases that let you use the raw disk partition instead
: of ordinary files.  We do real-time factory automation work, and it
: occurs to me that, if this is a significant speed win, this might be
: worth looking into for some of our own applications (particularly as
: I try to wrench my company away from DOS and toward SysVR4 for our
: work.)
: 
: What are the pitfalls in doing this?  Is it as easy programmatically
: as I envision (opening /dev/rdsk/<whatever> and using it as one big
: file)?  Is it even enough of a perfomance win to bother with?
: 
: Thanks in advance for any insight.
: 
: -- 
: Mark McWiggins			Integration Technologies, Inc. (Intek)
: +1 206 455 9935			DISCLAIMER:  I could be wrong ...
: 1400 112th Ave SE #202		Bellevue WA  98004
: uunet!intek01!mark		Ask me about C++!
: 

I have run Oracle Databases with Raw disk for production systems on heavily
loaded systems.  I must warn you that Raw disk uses the same Clist buffer
pool as terminals, and therefore your system must be appropriately tuned
to maintain data integrity.

UNIX systems are not very graceful about running out of system resources,
so you should plan for this requirement in advance.  Large blocks of data
moving to/from the Raw disk will steal Clist buffers at a much faster rate
than any terminal with typical flow control settings.  This means that your
seemingly abundant buffer pool could dwindle at a fantastic rate.

A typical symptom of exhausted Clists buffers would be losing characters
as they are being typed in, or blocks of data missing when you cat large
files to the terminal screen.  Now imagine that your screen is the Raw disk
device.  You should be able to see the extent of the exposure to data
integrity problems.

Another issue is speed.  On heavily loaded systems, I can measure no
*real world* difference in performance.  

					Martin Zam
					(201)564-2554