Re: The old raw devices chestnut.

"Jim Smith" <jim_at_jimsmith.demon.co.uk> wrote in message news:hq7AQQApjAfAFwlb_at_jimsmith.demon.co.uk...

> >
> >Is it faster I/O requests?
> >Or faster I/O overall?
> >Or less CPU used?
> >
>
> None of the above. A faster response and or throughput from a user point
> of view.

Nope. That has nothing to do with I/O speed.

> >eminently STUPID to claim "file system I/O" is faster: there is
> >no I/O in that case, just in-memory access!
>
> But it will give a faster response therefore "file systems are faster".

Absolutely not. Cache access is faster. And it has nothing to do with fs or raw I/O. You get EXACTLY the same speed regardless of where you got the data from.

> But, database blocks will often be buffered in the db buffer cache so
> the file system buffer may be irrelevant or even an overhead. I vaguely
> remember on VMS it was recommended you disable disk caching and used
> oracle's buffer cache.

Depends on what the OS can do. Some don't work all that well at doing direct I/O to/from buffer cache. And if they copy from another buffer, you end up with CPU use instead of I/O use.

-- 
Cheers
Nuno Souto
wizofoz2k_at_yahoo.com.au.nospam