On Sat, 11 Aug 2012, Chris Nagele wrote:


So far, running gnu dd with 512b and oflag=sync, the most we can get is 8k
iops on the zil device. I even tried with some SSDs (Crucial M4,

If this is one dd program running, then all you are measuring is "sequential" IOPS. That is, the next I/O will not start until the previous one has returned. What you want to test is threaded IOPS with some number of threads (each one represents a client) running. You can use iozone to effectively test that.

This command runs with 16 threads and 8k blocks with a 2GB file:

  iozone -m -t 16 -T -O -r 8k -o -s 2G

If you 'dd' from /dev/zero then the test is meaningless since zfs is able to compress zeros. If you 'dd' from /dev/random then the test is meaningless since the random generator is slow.

Is this the expected result? Should I be pushing for more? In IRC I
was told that I should be able to get 12k no problem. We are running
NFS in a heavily used environment with millions of very small files,
so low latency counts.

Your test method is not valid.

Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
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