High System Load

High System Load

[Huntress Gary B NPRI]

Hi,

I'm creating my first software RAID array.  I'm on a 900 MHz system with 786MB of ram, running Fedora RC1.  I'm creating a RAID 1 array consisting only of two drives, split on two IDE channels.

I used mdadm --create and everything is running fine so far, but my system load is well over 10.   Is this normal?   I suspect that this is just overhead while creating the array the first time.   Can I assume that when the array is actually put into use that the system loads will not be this high?  (I hope not!)

Thanks,

Gary H.

Re: High System Load

[Kanoa Withington]

There is a lot of activity after you first create a mirror but the CPU
load should not be that high. Maybe you don't have DMA turned on?
Check using "hdparm".

-Kanoa

On Wed, 28 Jul 2004, Huntress Gary B NPRI wrote:

> Hi,
>
> I'm creating my first software RAID array.  I'm on a 900 MHz system with 786MB of ram, running Fedora RC1.  I'm creating a RAID 1 array consisting only of two drives, split on two IDE channels.
>
> I used mdadm --create and everything is running fine so far, but my system load is well over 10.   Is this normal?   I suspect that this is just overhead while creating the array the first time.   Can I assume that when the array is actually put into use that the system loads will not be this high?  (I hope not!)
>
> Thanks,
>
> Gary H.
> -
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Re: High System Load

[Mike Hardy]

Even without DMA there should only ever be one kernel thread issuing 
instructions, resulting in a load of 1, which is all I've ever seen.

DMA vs. PIO modes will just result in a lower resync throughput, which 
you can watch with something like (you can even try using hdparm to 
change modes while the resync is happening to see the effect if you're 
brave):

#!/bin/tcsh
while 1
   cat /proc/mdstat
   sleep 1
   clear
end

There's got to be something else happening on the machine...

-Mike

Kanoa Withington wrote:
> There is a lot of activity after you first create a mirror but the CPU
> load should not be that high. Maybe you don't have DMA turned on?
> Check using "hdparm".
> 
> -Kanoa
> 
> On Wed, 28 Jul 2004, Huntress Gary B NPRI wrote:
> 
> 
>>Hi,
>>
>>I'm creating my first software RAID array.  I'm on a 900 MHz system with 786MB of ram, running Fedora RC1.  I'm creating a RAID 1 array consisting only of two drives, split on two IDE channels.
>>
>>I used mdadm --create and everything is running fine so far, but my system load is well over 10.   Is this normal?   I suspect that this is just overhead while creating the array the first time.   Can I assume that when the array is actually put into use that the system loads will not be this high?  (I hope not!)
>>
>>Thanks,
>>
>>Gary H.

Re: High System Load

[Jim Paris]

> #!/bin/tcsh
> while 1
>   cat /proc/mdstat
>   sleep 1
>   clear
> end

.. or just 'watch cat /proc/mdstat' :)

> There's got to be something else happening on the machine...

I find that if the kernel variable dev.raid.speed_limit_max is too
high (the default, 200000, is usually too high), then the rebuild
could taking all available I/O time.  This can cause every other
process trying to do I/O on the machine to block, which may be the
reason your load average is so high.

Try doing 'sysctl -w dev.raid.speed_limit_max=10000' and see if things
improve.

-jim