Re: O_DIRECT question

[Michael Tokarev]

Phillip Susi wrote:
> Denis Vlasenko wrote:
>> You mean "You can use aio_write" ?
> 
> Exactly.  You generally don't use O_DIRECT without aio.  Combining the
> two is what gives the big win.

Well, it's not only aio.  Multithreaded I/O also helps alot -- all this,
say, to utilize a raid array with many spindles.

But even single-threaded I/O but in large quantities benefits from O_DIRECT
significantly, and I pointed this out before.  It's like enabling a write
cache on disk AND doing intensive random writes - the cache - surprizingly -
slows whole thing down by 5..10%.

/mjt
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