From owner-freebsd-stable@FreeBSD.ORG  Mon Jun  7 05:15:04 2010
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From: "Dewayne Geraghty" <dewayne.geraghty@heuristicsystems.com.au>
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Date: Mon, 7 Jun 2010 11:57:47 +1000
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Subject: RE: AHCI timeouts - 8.1-PRERELEASE
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Quick update.
Following extensive testing, I've recommended to Alexander, in a 
longer email, that the default for VIA's VT8251 AHCI Controller 
be set at AHCI_Q_NOPMP|AHCI_Q_NONCQ

Use of ahci in the kernel without this option will result in timeouts, 
ultimately preventing the machine from performing IO. No timeouts 
occurred when the ahci driver was removed from the kernel.

Approx 35 tests were applied, simultaneously copying a large number 
of files (~2000) to 8 partitions that ranged in size from 10B to 1.6GB.
Testing included single and gmirror disks.  

The removal of NCQ resulted in a degraded performance of < 8% when 
compared against EDGEIS, which failed under gmirror testing.  
Performance under load without NCQ was better than a kernel 
without ahci.

The test was conducted on a VIA SN18000 using two WD500GB-AAKS disks, 
the disks were repartitioned (gpart) and system rebooted before each test.

Regards, Phil.