On Nov 16, 2007 10:41 PM, Neil Perrin <[EMAIL PROTECTED]> wrote: > > > Joe Little wrote: > > On Nov 16, 2007 9:13 PM, Neil Perrin <[EMAIL PROTECTED]> wrote: > >> Joe, > >> > >> I don't think adding a slog helped in this case. In fact I > >> believe it made performance worse. Previously the ZIL would be > >> spread out over all devices but now all synchronous traffic > >> is directed at one device (and everything is synchronous in NFS). > >> Mind you 15MB/s seems a bit on the slow side - especially is > >> cache flushing is disabled. > >> > >> It would be interesting to see what all the threads are waiting > >> on. I think the problem maybe that everything is backed > >> up waiting to start a transaction because the txg train is > >> slow due to NFS requiring the ZIL to push everything synchronously. > >> > > > > I agree completely. The log (even though slow) was an attempt to > > isolate writes away from the pool. I guess the question is how to > > provide for async access for NFS. We may have 16, 32 or whatever > > threads, but if a single writer keeps the ZIL pegged and prohibiting > > reads, its all for nought. Is there anyway to tune/configure the > > ZFS/NFS combination to balance reads/writes to not starve one for the > > other. Its either feast or famine or so tests have shown. > > No there's no way currently to give reads preference over writes. > All transactions get equal priority to enter a transaction group. > Three txgs can be outstanding as we use a 3 phase commit model: > open; quiescing; and syncing. >
anyway to improve the balance? Is would appear that zil_disable is still a requirement to get NFS to behave in an practical "real world" way with ZFS still. Even with zil_disable, we end up with periods of pausing on the heaviest of writes, and then I think its mostly just ZFS having too much outstanding i/o to commit. If zil_disable is enabled, is the slog disk ignored? > Neil. > > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
