>> Now, I understand that normally, Linux does not allow access to raw
>> disk devices, but this is a case where I want to test the hardware
>
>The notion of 'raw' disk is foreign to Linux. Its a Unixism. The block device
>interface is used instead. That isnt optimised for performance however (ie
>heavy readahead etc)
Since sending out that note, I've had this explained to me. Can you
explain to me the semantics of an Oracle or Sybase database wanting to
have direct access to a raw disk device for the database, so that:
1) You don't trash your buffer cache
2) You don't waste your time and that of the database when it
could avoid the filesystem redirection entirely?
Or am I mistaken in believing that the block device interface is also
pumped through the vm/buffer cache system?
What about the implications of someone that wants to tune each
subsystem for maximum performance, without having other aspects of the
system interfere with that testing? It would seem to me that you're
assuming that you folks know more about all possible uses of Linux and
how to best tune the system for all those uses, than anyone who could
possibly come along and want to use a Linux system for a particular purpose.
To that degree, it would seem to me that Linux is considerably less
useful as a server, precisely because anyone who is not a Kernel hacker
can't get real low-level control of the system so that they can tune it
to the nth degree -- or for that matter, even just benchmark the thing,
and compare the performance of say software mirroring/striping/RAID
against older and newer hardware controllers to achieve the same goals.
Thanks! I appreciate any insights you may have.
--
Brad Knowles <brad@shub-internet.org> <http://www.shub-internet.org/brad/>
<http://wwwkeys.pgp.net:11371/pks/lookup?op=get&search=0xE38CCEF1>
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