Date: Fri, 11 Apr 2008 16:01:56 -0500 From: Karl Denninger <karl@denninger.net> To: freebsd-stable@freebsd.org Subject: Re: Disk I/O Question 7.0-STABLE Message-ID: <20080411210156.GA89281@FS.denninger.net> In-Reply-To: <20080411093316.GA31354@voi.aagh.net> References: <20080410223153.GA336@FS.denninger.net> <20080411093316.GA31354@voi.aagh.net>
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On Fri, Apr 11, 2008 at 10:33:16AM +0100, Thomas Hurst wrote: > * Karl Denninger (karl@denninger.net) wrote: > > > I have disks on the internal ICH7 adapters (on the motherboard), SATA, > > and also a TWE controller with two disks. > > > > When hitting the TWE controller hard I can hose the I/O performance on > > the primary (onboard) adapter quite severely to the point that it > > seriously impairs the system's overall performance. "systat -vm" > > shows the primary channels going to 100% busy but the transaction and > > I/O rate count is not all that high. The twe disk I am hammering, of > > course, is saturated (and blowing data at a high rate of speed - > > 70MBps+) > > I see exactly the same behavior on a dual dual core AMD box using amr(4) > (8 port LSI MegaRAID SATA) and an 8 port Marvell 88SX6081 ata(4) > controller. I have 3 RAID-1 arrays configured on the LSI and a single > drive on the Marvell; I can freeze up IO to all of them for several > seconds just by running find / >/dev/null for up to 30s. > > gstat shows the IO queue for one drive in the high hundreds (all > writes), and it seems waiting for it to flush is what kills the rest of > the system. > > My best guess is this is a result of the syncer flushing atime updates. > I should try mounting my /usr noatime and seeing if the problem goes > away. Not the greatest of solutions, but meh. Mounting with noatime does help a bit but does NOT prevent the problem from showing up. Note that softupdates is OFF on the disk that is being hammered when everything goes to hell so its not a buffer flushing problem there either. -- -- Karl Denninger (karl@denninger.net) Internet Consultant & Kids Rights Activist http://www.denninger.net My home on the net - links to everything I do! http://scubaforum.org Your UNCENSORED place to talk about DIVING! http://genesis3.blogspot.com Musings Of A Sentient Mind
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