On Wed, Oct 03, 2007 at 10:42:53AM +0200, Roch - PAE wrote: > Rayson Ho writes: > > 2) Also, direct I/O is faster because it avoid double buffering. > > A piece of data can be in one buffer, 2 buffers, 3 > buffers. That says nothing about performance. More below. > > So I guess you mean DIO is faster because it avoids the > extra copy: dma straight to user buffer rather than DMA to > kernel buffer then copy to user buffer. If an I/O is 5ms an > 8K copy is about 10 usec. Is avoiding the copy really the > most urgent thing to work on ?
If the DB is huge relative to RAM, and very busy, then memory pressure could become a problem. And it's not just the time spent copying buffers, but the resources spent managing those copies. (Just guessing.) _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
