From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Jarosch <thomas.jarosch@intra2net.com>
Subject: Re: Incredibly poor performance of mdraid-1 with 2 SSD Samsung 840 PRO
Date: Thu, 25 Apr 2013 13:38:17 +0200
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To: Andrei Banu <andrei.banu@redhost.ro>
Cc: linux-raid@vger.kernel.org
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On Sunday, 21. April 2013 02:26:26 Andrei Banu wrote:
> They are connected through SATA2 ports (this does explain the read speed
> but not the pitiful write one) in AHCI.

So the SATA controller is already in AHCI mode. Good.

You didn't say what kind of server hardware you are using or I missed it.
On the HP DL3xxx servers we usually use, we have to enable AHCI mode _and_ 
the write cache in the BIOS. Maybe your server needs something similar.

Some RAID controllers only allow you to enable the write cache
when a battery-backed write cache module is installed.

HTH,
Thomas