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. Neil. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
