Scott Marlowe wrote: > On Tue, Oct 6, 2009 at 8:26 AM, Scott Marlowe <scott.marl...@gmail.com> wrote: > >> On Tue, Oct 6, 2009 at 7:21 AM, Nikolas Everett <nik9...@gmail.com> wrote: >> >>> If my un-word wrapping is correct your running ~90% user cpu. Yikes. Could >>> you get away with fewer disks for this kind of thing? >>> >> Probably, but the same workload on a 6 disk RAID-10 is 20% or so >> IOWAIT. So somewhere between 6 and 12 disks we go from significant >> IOWAIT to nearly none. Given that CPU bound workloads deteriorate >> more gracefully than IO Bound, I'm pretty happy having enough extra IO >> bandwidth on this machine. >> > > note that spare IO also means we can subscribe a slony slave midday or > run a query on a large data set midday and not overload our servers. > Spare CPU capacity is nice, spare IO is a necessity. > > More importantly when you run out of I/O bandwidth "bad things" tend to happen very quickly; the degradation of performance when you hit the IO wall is extreme to the point of being essentially a "zeropoint event."
-- Karl
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