Date: Thu, 13 Jun 2002 11:32:59 -0500 From: Dan Nelson <dnelson@allantgroup.com> To: "Brian T.Schellenberger" <bts@babbleon.org> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: Write-cache control for SCSI? Message-ID: <20020613163259.GA37481@dan.emsphone.com> In-Reply-To: <20020613112509.C3E78BB2C@i8k.babbleon.org> References: <20020613112509.C3E78BB2C@i8k.babbleon.org>
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In the last episode (Jun 13), Brian T.Schellenberger said:
> I know that ATA device control write cache with
>
> sysctl hw.ata.wc
>
> but what do I use to control/check write caching with the a SCSI device?
Caching is a per-device setting stored on the drive itself; you only
need to set it once, and the drive will remember it forever. I've
attached a script that will check all the SCSI disks on your system and
warn you if WCE is enabled.
> (And, for that matter, DMA -- or does that not apply to the SCSI world?)
DMA is purely a matter between the motherboard and the SCSI card, and
unless you're running a 10-year-old ISA Adaptec 1520, is always used.
--
Dan Nelson
dnelson@allantgroup.com
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#! /bin/sh
echo Checking SCSI drives for write-cache:
numbad=0
# get a list of direct-access devices known to the system
units=$(camcontrol devlist | sed -n -e "/,da[0-9]*/s/^.*(.*\(da[0-9]*\)).*$/\1/p")
for i in $units
do
if camcontrol modepage $i -m 8 -P 3 2> /dev/null | grep -q "WCE:.*1" ; then
camcontrol devlist | grep "(.*$i.*)"
numbad=$(($numbad + 1))
fi
done
if [ $numbad -gt 0 ] ; then
s=
[ $numbad -ne 1 ] && s=s
echo "
$numbad device$s with WCE set. To reset, run
\"camcontrol modepage <device> -e -P 3 -m 8\"
where <device> is the disk name (i.e. da0), and set WCE to 0."
fi
echo
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