Re: [GENERAL] full_page_writes = off?

I thought we had the disk write cache control documented for popular
operating systems, but I see we don't so I added the following patch to
our documentation.

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Greg Smith wrote:
> 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(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD
>
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--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://postgres.enterprisedb.com

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