Message-ID: <4DFC1351.2000002@2ndQuadrant.com>
Date: Fri, 17 Jun 2011 22:54:09 -0400
From: Greg Smith <greg@2ndQuadrant.com>
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To: pgsql-docs@postgresql.org
Subject: Re: Small correction in
	http://www.postgresql.org/docs/9.0/interactive/wal-reliability.html
References: <201106171455.45391.achill@matrix.gatewaynet.com>
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On 06/17/2011 07:55 AM, Achilleas Mantzios wrote:
> It reads :
> 'On FreeBSD, IDE drives can be queried using atacontrol, and SCSI drives using sdparm.'
> but it should be:
> 'On FreeBSD, IDE drives can be queried using atacontrol, and SCSI drives using camcontrol.'
>    

FreeBSD's Common Access Method (CAM) looks to be the preferred driver 
layer to interrogate.  sdparm is available on Linux and FreeBSD, but 
it's a second-class citizen talking to CAM on the latter.  To quote from 
one of the docs on it, FreeBSD sdparm "SCSI commands are routed through 
the CAM pass-through interface".  Talking directly to it with camcontrol 
does seem to be the preferred route for some things.

However, the UI to sdparm is a bit easier to use when it is available.  
Actually changing the write cache state with camcontrol requires black 
magic--you have to construct the right SCSI packet by hand.  I can't 
find any example.

Bruce just touched this section of the docs recently, so this part 
actually reads just:

          SCSI drives use <command>sdparm</command>.

Now.  Perhaps the following makes sense:

          SCSI drives can be queried using <command> camcontrol 
identify</command>, and the write cache both queried and changed using 
<command>sdparm</command> when available.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us