From: Greg Smith <gsmith@gregsmith.com>
To: pgsql-general@postgresql.org
Subject: Re: full_page_writes = off?
Date: Sun, 2 Dec 2007 15:58:56 -0500 (EST)
Message-ID: <Pine.GSO.4.64.0712021528290.2007@westnet.com> (raw)
In-Reply-To: <20071201121601.GB2552@batory.org.pl>
References: <4751150F.8080604@mail.ru>
<20071201114754.GA2552@batory.org.pl>
<47514DDC.70607@marquesminen.com.ar>
<20071201121601.GB2552@batory.org.pl>
On Sat, 1 Dec 2007, Tomasz Ostrowski wrote:
> You can also use "hdparm -I" to check this - look for a "Write
> caching" in "Commands/features" section. If it has a "*" in front
> then it is enabled and dangerous.
Right; using -I works with most Linux hdparm versions:
# hdparm -V
hdparm v6.6
# hdparm -I /dev/hda | grep "Write cache"
* Write cache
# hdparm -W 0 /dev/hda
/dev/hda:
setting drive write-caching to 0 (off)
# hdparm -I /dev/hda | grep "Write cache"
Write cache
While being able to check the state with -W only works in very recent
ones.
The best way to make this change permanent varies depending on your Linux
distribution.
Also: nowadays many SATA disks appear as SCSI devices like /dev/sda. In
some cases I believe you can use a recent hdparm on them anyway, in others
I've had to use sdparm instead. Several of the examples at
http://sg.torque.net/sg/sdparm.html show how to manipulate the Write Cache
Enabled (WCE) status similarly to the above on SCSI devices.
> I don't know how to check it on BSD.
In FreeBSD I believe you use atacontrol to check the settings, and you can
make the changes permanent by fiddling with the /boot/device.hints file.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
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To: pgsql-docs@postgresql.org
Cc: gsmith@gregsmith.com, pgsql-general@postgresql.org
Subject: Re: full_page_writes = off?
In-Reply-To: <Pine.GSO.4.64.0712021528290.2007@westnet.com>
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