Joao,

Wow, thanks for doing this!

In general, your tests seem to show that there isn't a substantial penalty for using ZFS as of version 8.0.

If you have time for more tests, I'd like to ask you for a few more tweaks:

(1) change the following settings according to conventional wisdom:
        wal_buffers = 8MB
        effective_cache_size = 9GB
        checkpoint_segments = 32
        on ZFS only: full_page_writes=off

(2) What scale were you using for the pgbench database? I didn't see it in the e-mail. It would be worth testing:
        s = 10 (small database, in memory)
        s = 500 (7GB, ram mostly full)
        s = 1000 (14GB, slightly larger than ram)
        s = 3000 (43GB, much larger than ram)

If you were only testing a small size in your runs, then the only Filesystem behavoir you were testing was the transaction log.

(3) Try a ZFS 128K record size

(4) Centos/Ext3 appears to have had better staying power with high numbers of clients. Can you continue testing with 50, 100 and 200 clients on that combination? And with data=writeback,noatime on Ext3?

--
                                  -- Josh Berkus
                                     PostgreSQL Experts Inc.
                                     http://www.pgexperts.com

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