megaraid causing high-load

David Lucas dlucas at comsltd.com
Wed Mar 9 08:08:01 CST 2005


Jason,

> the first things i'd check are making sure you have the latest 
> firmware on
> your controller.  in my experience the load average normally rises 
> when you
> find the system is queueing requests - i.e it can't read or write fast 
> enough
> to keep up or the other side, it can't push the data out fast enough (the
> network interface for example is congested).  you can sometimes catch 
> this using iostat (though not very reliably :-/) and watching for a 
> while at
> the avgrq-sz avgqu-sz await values.

I have been catching pend_cmds != 0 requests by watching 
/proc/megaraid/hba0/stat

> The load never really drops low ... always hovering around the 
> 0.10-0.40 mark even when the system is barely idle.
>
> heh.  on our fileserver.
>
>  14:03:48  up 70 days, 4 min,  2 users,  load average: 75.99, 85.89, 
> 86.02
>
> 0.1-0.4 is busy ? you're kidding me right ? :-)

Considering it is doing next to NOTHING, I would expect a near 0 load. I 
am just in the process of configuring it for an inhouse mail and other 
file services and it is sluggish beyond reason!!! However, I must say 80 
is good ;)

> i'm assuming 1G here..

I chatise people myself for this error and here I go making it ... yes, 
of course 1G

> i wouldn't turn off swap myself.. but there may be some tuning that is 
> required.

The system is barely loaded at the moment ... turning swap off was an 
attempt to see if this was a potential problem area (which is was not)

> increase the memory to start with - i've found that increased 
> buffering usually
> helps significantly with i/o queueing.  i'd go to 2 or even 4G if you 
> could.
>
> you haven't said too much else about what you're doing on the server.. 
> so it's
> hard to say much more about tuning it.. and unfortunately most of my 
> tuning
> stuff is all for 2.4 :-/

Basically the server is doing next to nothing ... inhouse fileserver and 
mail for about 5 accounts.  I would neverhave spec'd a machine so high, 
but it was what they had!!!  My prob is that it performs far worse than 
even my PIII 450 at home serving more!!! The only reason I think it 
performs at all is that is has 1Gb of mem, of which 75% is used as I/O 
cache!

Still working on it ;)

Thanks
David
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