PE6650 Disk I/O performance under Linux

Darrin Hyrup shades at
Mon Aug 26 15:21:00 CDT 2002

Greetings all,

We have been considering upgrading some of our more heavily-utilized Linux 
database servers to the PowerEdge 6650 platform (under RH7.3) to take 
advantage of the additional processors, hyperthreading, et al.  But, I am 
reluctant to do so, as one common problem that is always brought up when 
talking about Dell servers is that they are disk I/O bound due to slower 
RAID functionality.  So, moving to a faster machine may not really help 
performance after all since the new servers are probably limited by the 
speed of the RAID subsystem so any increase would be negligible.  We don't 
want to invest a lot of money into a solution unless it will really give us 
a dramatic boost in performance.

Our current (PE2550/RH7.2) servers are generally quite responsive, but 
intensive queries can bring them to their knees pretty easy.  We've got 
plenty of RAM and running 15k RPM drives, so I'm sure the non-RAID hardware 
is probably fine.  The applications utilizing these servers have very 
little tolerance for long delays on query responses, so boosting the top 
end to better handle those spikes would be very nice.  (The databases 
themselves are already optimized for speed where they can be.)

My questions are whether or not there is anything we can do to reduce disk 
I/O bottleneck using Dell components?  Is there a better RAID card that we 
can get bundled with these machines through Dell (or even 3rd party if 
necessary) that would improve this issue, or are we better off using the 
additional processor power to run a software RAID 5 setup?  As a matter of 
comparison, how much of an improvement would we expect to see if we made 
similar changes to our existing hardware instead (and/or upgrading PE2650s 
rather than 6650s?)  That would certainly reduce costs (since those 6650s 
are not cheap.)  My gut instinct is to avoid using software RAID on 
database servers since they need all the CPU they can get, but if it is the 
better solution, so be it.

I also assume that any Dell provided solution would also work with the 
built-in diagnostic displays built into the PE2650/6650 chassis?  I suspect 
that software RAID or 3rd-party add-in card status would not be reflected 
by that display, and those displays have come in handy in the past.

I'm hoping others on this list have dealt with similar issues in the past 
and may be able to offer some advice or even specific recommendations on 
what has worked in the past for others.  I need to make a recommendation 
one way or the other this week, so any comments and/or suggestions are 


Darrin Hyrup
Mythic Entertainment

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