On May 19, 2009, at 8:56 PM, Nicholas Lee wrote:
So txg is sync to the slog device but retained in memory, and then rather than reading it back from the slog to memory it is copied to the pool from memory the copy?
Yes, that is correct. It is best to think of the ZIL and the txg sync process as orthogonal - data goes to both locations at different times. The ZIL (technically "all ZILs" since they're per-filesystem) is *only* read in the event of log replay (unclean shutdown). During normal operation it is never read. Hence the benefit of write-biases SSDs - it doesn't matter if reads are fast for slogs.
With the txg being a working set of the active commit, so might be a set of NFS iops?
If the NFS ops are synchronous, then yes. Async operations do not use the ZIL and therefore don't have anything to do with slogs.
- Eric -- Eric Schrock, Fishworks http://blogs.sun.com/eschrock _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
