On Thu, 24 Sep 2009, James Lever wrote:
I was of the (mis)understanding that only metadata and writes smaller than 64k went via the slog device in the event of an O_SYNC write request?
What would cause you to understand that?
Is there a way to tune this on the NFS server or clients such that when I perform a large synchronous write, the data does not go via the slog device?
Synchronous writes are needed by NFS to support its atomic write requirement. It sounds like your SSD is write-bandwidth bottlenecked rather than IOPS bottlenecked. Replacing your SSD with a more performant one seems like the first step.
NFS client tunings can make a big difference when it comes to performance. Check the nfs(5) manual page for your Linux systems to see what options are available. An obvious tunable is 'wsize' which should ideally match (or be a multiple of) the zfs filesystem block size. The /proc/mounts file for my Debian install shows that 1048576 is being used. This is quite large and perhaps a smaller value would help. If you are willing to accept the risk, using the Linux 'async' mount option may make things seem better.
Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
