Hi
On Sat, 5 Sep 2009 18:52:35 -0600, dan <dandenson AT gmail DOT com> wrote:
> > the "perfect" max load should be the number of cpus you have,
> > so a quad-core server can sustain a load of 4 without any
> > problem... after that number, the higher the load, the higher
> > will be the performance lost
> I dont agree here at all. backuppc is not generally CPU bound. If
> your target is to max out a quad core then you really need to beef up your
i'm not saying that backuppc is cpu bound, i'm describing what
is the "perfect" load, as he asked...
the "s in the perfect is because its not the only metric needed
to check how a machine is going, but is one of the most important.
the load is the number of process requiring CPU during a set of
time, but isnt just equal to the % of cpu usage, other
operations, like IO, require cpu slots even if they dont really
use cpu (DMA transfers and like). If load=# of cpus, no process
is waiting for cpu slot, when load > # cpus, you have process
that will be waiting for cpu slot in each cpu cycle...
the higher the load, the more process will be stopped, waiting
for their turn to use a cpu slot
He have a load of 9, we dont know how much cpu he have, but
even if its a quad-core, seems to me a high load, so he is
probably running too much concurrent backups at same time.
for sure the problem is in the IO, not in the cpu, but the
load shows that is doing more work than he can manage.
Solving the bottleneck (in this case is adding more disks for
sure) will decrease the load, as each operation will terminate
sooner and freeing the cpu slots for other process
> You make a lot more sence here, but I think you overestimate CPU usage.
see above :)
> a dual core 2Ghz Opteron with 2GB of ram and 8 drives in a linux raid10
> and hard disk speed is still my bottleneck. I run 4 concurrent backups
> on that machine and it does give high system load numbers but still
> handles the desktops in the office faster than 3 concurrent while 5
> concurrent takes quite a bit longer to complete.
how much is the "high system load"?
have you checked the 15 minutes load average with 3, 4 and
5 concurrent backups?
i suspect that with 3, you have a load around 1.5, with 4,
a load around 2.5, with 5, a load around 4.5... that is, you
are getting a higher jump from 4 to 5 than from 3 to 4
having a load of 6 during one minute isnt important, if its
just one minute
but again, load isnt the only metric, iostat gives the rest
of the info needed.
> filesystem choice and
> io scheduler do make a difference but faster disks is the only real
> cure.
faster HD or more disk to spread the load for more HDs...
for most people, this is true
cya
higuita
--
Naturally the common people don't want war... but after all it is the
leaders of a country who determine the policy, and it is always a
simple matter to drag the people along, whether it is a democracy, or
a fascist dictatorship, or a parliament, or a communist dictatorship.
Voice or no voice, the people can always be brought to the bidding of
the leaders. That is easy. All you have to do is tell them they are
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