On Thu, Apr 03, 2008 at 07:21:54AM -0700, malahal@xxxxxxxxxx wrote: > Heinz Mauelshagen [mauelshagen@xxxxxxxxxx] wrote: > > > > [HM] md RAID456 and dm RAID45 don't have the raid1 problem, because > > they utilize stripe caches, hence tacking page copies. Application pages > > can change nonetheless vs. stripe cache pages. > > I wish they didn't make copies of data pages for the sake of > performance! If they did make copies for all of their I/O, they don't > have this problem. Me too but it's mandatory to be able to calculate parity chunks ;) > > > > 4. make more region states. > > > --- If the region is in RH_DIRTY state and all writes drain, the state is > > > changed to RH_MAYBE_DIRTY. (we don't know if the region is synchronized or > > > not). The disk dirty flag is kept. > > > --- periodically (once in few minutes, so that it doesn't affect > > > performance much), the change all regions in RH_MAYBE_DIRTY state to > > > RH_CLEAN_CANDIDATE, then issue sync() on all filesystems. If, after the > > > sync(), the region is still in RH_CLEAN_CANDIDATE (i.e. it hasn't been > > > written during the sync()), it is moved to RH_CLEAN state and the on-disk > > > bit for the region is turned off. > > > > [HM] This is essentially one technical approach for my comment on 2. above. > > RH_MAYBE_DIRTY sounds superfluous at first glance, because when all writes > > to a region drained, we can set RH_CLEAN_CANDIDATE, run the sync() and check > > if that state persists in order to trigger the dirty log update. > > I don't think the state RH_MAYBE_DIRTY is superfluous. If the region > state is RH_CLEAN_CANDIDATE after the sync(), that means no 'write' > happened since we set RH_CLEAN_CANDIDATE. If there was any write, the > region state would be 'RH_DIRTY' or 'RH_MAYBE_DIRTY'. Hrm, sound like a contradiction in your statement. Either it stays RH_CLEAN_CANDIDATE because of no writes *or* it's state-changing to RH_DIRTY, no ? Heinz > > --Malahal. > > -- > dm-devel mailing list > dm-devel@xxxxxxxxxx > https://www.redhat.com/mailman/listinfo/dm-devel -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
