On Tue, Nov 3, 2009 at 4:37 PM, Chris Worley <worleys@xxxxxxxxx> wrote: > On Tue, Nov 3, 2009 at 5:29 PM, Michael Evans <mjevans1983@xxxxxxxxx> wrote: >>> >>> 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. > > Stripe_cache_size doesn't seem to exist in the /sys/block/md*/md/ > directory on the RHEL5.3 2.6.18-92 kernel I'm using. > > # ls /sys/block/md*/md/s* > /sys/block/md0/md/safe_mode_delay /sys/block/md0/md/suspend_hi > /sys/block/md0/md/suspend_lo /sys/block/md0/md/sync_action > /sys/block/md0/md/sync_completed /sys/block/md0/md/sync_speed > /sys/block/md0/md/sync_speed_max /sys/block/md0/md/sync_speed_min > > Thanks, > > Chris >> > I'm not sure when it was added, but I've =no= idea the number of bugs that may have been fixed since then. You should look at the other files in that virtual directory to see if there's another parameter that it replaced. -- 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
