From owner-freebsd-fs  Fri Oct  2 18:25:45 1998
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Date: Sat, 3 Oct 1998 11:24:50 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199810030124.LAA18635@godzilla.zeta.org.au>
To: Don.Lewis@tsc.tdk.com, gibbs@plutotech.com
Subject: Re: filesystem safety and SCSI disk write caching
Cc: freebsd-fs@FreeBSD.ORG, freebsd-scsi@FreeBSD.ORG
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>>BTW, with softupdates, and tagged command queuing enabled in CAM, there
>>is not much of a performance hit from turning off write caching.  I
>>saw "make buildworld" increase from about 2 hours to 2 hours 5 minutes,
>>and "make -j6 buildworld" increase from about 1 hour 30 minutes to
>>1 hour 35 minutes.
>
>In this particular benchmark, perhaps not, but make buildworld is not
>indicative of most I/O loads.

I think it can be interpreted as showing that the performance hit is
very large.  `make world' is mostly cpu-bound, and most of it's i/o's
are reads (60% here).  I guess it spends less than 5 minutes of its time
writing (27000 block output operations here).  An increase of 5 minutes
is very large.

Bruce

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