> > So, you're saying that the MD layer is doing it's own buffering? Are > you sure? With the system cache disabled and the drive (and block > device driver) cache disabled, there should be no reason to require > synchronous I/O, unless, as you suggest, the MD layer is broken. > > You're saying that both O_DIRECT and O_SYNC must be used to disable > cache effects. Why then are there two separate flags and not just one? > Synchronous is a very different behavior that is not necessary for > this test and put additional requirements that are not needed for this > test. > > Chris > Reading the manual page it seems O_DIRECT explicitly minimizes any attempts at extra copying; not explicitly disabling buffers, merely not adding more. In another mail thread this tweak-able was discussed: echo 0 > /sys/block/md*/md/stripe_cache_size Which would should (I think) disable any cache involved with the md layer. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
