Date: Sat, 16 Apr 2005 14:54:31 -0500 From: Eric Anderson <anderson@centtech.com> To: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: gstat shows > 100% busy Message-ID: <42616D77.2070205@centtech.com> In-Reply-To: <3703.1113680811@critter.freebsd.dk> References: <3703.1113680811@critter.freebsd.dk>
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Poul-Henning Kamp wrote: > In message <42616975.9060303@centtech.com>, Eric Anderson writes: > > >>Is gstat supposed to show > 100% sometimes? What does that mean, >>or is it a bug? >> >>dT: 0.501 flag_I 500000us sizeof 240 i -1 >> L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name >> 2 260 146 14912 10.7 114 14565 2.8 148.1| ad0 >> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1 > > > The reason gstat shows >100% busy is that there are some outstanding > requests. (the 2 in the left hand column). > > I tried to make the statistics collection as cheap as possible, and > as a side effect some of the columns can be somewhat misleading. Makes perfect sense, and I was thinking that was the case. I love how fast and non-cpu intensive it is. I use this tool like *crazy* on my servers. Thanks for writing it! > The length of the queue "L(q)" can be plain wrong due to a race in > updating the counters and %busy can go over 100% while there are > outstanding requests. > > The sysctl kern.geom.collectstats can be used to tune some aspects > of the statistics collection, but the %busy issue is just something > you have to live with. > > The reason why I don't want to spend cpu time on the %busy field > is that it is useless as a performance indication for all modern > disks and most ancient ones as well. Why is that? I have a general notion, but I'd like to know more details. If this is documented somewhere, just give me a pointer and I'll read away. > The "ms/r" and "ms/w" give you the time it takes to send a transaction > through (in milliseconds, for read and write respectively) and those > are the numbers you should monitor. Thanks! I've been reading man pages and such trying to figure out what else is cool I'm missing. I just happened to stumble into the tool while messing with ggate (another really awesome tool). Is there a place to grab those stats in a more 'script friendly' way? I am the author of a (rather cheesy) tool called bsdsar, and I'm thinking about updating it with all the new cool 5.X-isms. Thanks for the quick responses! Eric -- ------------------------------------------------------------------------ Eric Anderson Sr. Systems Administrator Centaur Technology A lost ounce of gold may be found, a lost moment of time never. ------------------------------------------------------------------------
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