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In-reply-to: Your message of "Thu, 23 Nov 2006 02:52:15 EST."
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Date: Thu, 23 Nov 2006 09:35:08 +0000
From: Dieter <freebsd@sopwith.solgatos.com>
Subject: Re: processes not getting fair share of available disk I/O (was:
	Re: TCP parameters and interpreting tcpdump output ) 
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> > > > 	hw.ata.wc=3D3D0
> > >         ^^^^^^^^^^^
> > > "Make my hard drive go reeeeally slow please (just in case I crash)" :)
> >=20
> > Slower, yes, but not *that* slow.
> >=20
> > Normal ls : 0.032 second.  Two processes using same disk, multiply by two,
> > so 0.064 second.  Maybe the multiplier is more than 2, call it 10x, so
> > 0.32 second.  But I'm seeing a factor of over 9100x.
> 
> Humour me and turn it back on, then see what happens.

Where is the knob to turn the write cache on/off on a per-drive basis
in FreeBSD?  I can do this in NetBSD, but the only knob I can find in
FreeBSD affects all drives, and requires a reboot.

Humour me and read the Subject line.  The ls does not get its fair share
of disk I/O.

Both times are with the disk's write cache in write-through mode.
I'm not comparing times with the write cache in different modes.
I'm comparing ls by itself against ls competing with cp.