Best filesystem for a high load db

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Hello,
I need to install a Postgresql 9.4 cluster with two servers at first
instance. The database will be used in an enviroment with high load, a
lot number of clients will do queries that require fast replies.
I have to install Ubuntu 14.04 as OS and I would like to know which
filesystem you would suggest me to use. I have read that ZFS with ZIL
is now mature for a production server: do you think it is that true or
that it would be better to stay safer with a common EXT4?

Thanks in advance.

Maila Fatticcioni
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