On 25/09/2009, at 1:24 AM, Bob Friesenhahn wrote:
On Thu, 24 Sep 2009, James Lever wrote:
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.
From the Linux NFS FAQ. http://nfs.sourceforge.net/
NFS Version 3 introduces the concept of "safe asynchronous writes.”
And it continues.
My rsize and wsize are negotiating to 1MB.
James
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