Scott Marlowe wrote:
On Tue, Oct 6, 2009 at 8:26 AM, Scott Marlowe <scott.marlowe@gmail.com> wrote:
On Tue, Oct 6, 2009 at 7:21 AM, Nikolas Everett <nik9000@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