On Tue, November 8, 2011 09:38, Evaldas Auryla wrote:
> I'm trying to evaluate what are the risks of running NFS share of zfs
> dataset with sync=disabled property. The clients are vmware hosts in our
> environment and server is SunFire X4540 "Thor" system. Though general
> recommendation tells not to do this, but after testing performance with
> default setting and sync=disabled - it's night and day, so it's really
> tempting to do sync=disabled ! Thanks for any suggestion.
You may want to examine getting some good SSDs and attaching them as
(mirrored?) "slog" devices instead:
http://www.solarisinternals.com/wiki/index.php/ZFS_Best_Practices_Guide#Separate_Log_Devices
You probably want to zpool version of 22 or better to do this, as from
that point onward it becomes possible to remove the "slog" device/s if
desired. Previous to v22 once you add them you're stuck with them.
Some interesting benchmarks on offloading the ZIL can be found at:
https://blogs.oracle.com/brendan/entry/slog_screenshots
Your SSD/s don't have to be that large either: by default the ZIL can be
at most 50% of RAM, so if your server has (say) 48 GB of RAM, then the an
SSD larger than 24 GB would really be a bit of a waste (though you can use
the 'extra' space as L2ARC perhaps). Given that, it's probably better
value to get a faster SLC SSD that's smaller, rather than a 'cheaper' MLC
that's larger.
Past discussions on zfs-discuss have favourably mentioned devices based on
the SandForce SF-1500 and SF-2500/2600 chipsets (they often come with
supercaps and such). Intel's 311 could be another option.
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