Tuning the configuration

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Hello.
I need to tune a postgres installation I've just made to get a better
performance. I use two identical servers with a hot replication
configuration. The two servers have the following hardware:

Dual Processor Intel Xeon E5-2640V2 20Mb cache 2.00Ghz,
Ram Mem. 32Gb DDR-3 Ecc Registered,
Controller MegaRaid 8-ports 1Gb cache,
4 Enterprise Hdd NL Sas 600 4Tb Sata,
2 Samsung SSD 840 Pro Series 512Gb,
2 Hdd 500 Gb

I made a software raid with the last two hard disks with ext4 and I
installed Ubuntu 14.04.1 LTS (I have to use this SO) on it. I made a
hardware raid with the four SAS hard disks and I mount the partition
on it with ext4 without journaling and I put the database on it.

Now I have two more steps to do.

1- could you please help tuning the configuration? What are the best
value I should use for wal_buffers and shared_buffers?
2- I would like to use the two SDD to store the wal file. Do you think
it is useful or how should I use them?

Thank you for your answers.

Best Regards,
Maila Fatticcioni
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