Re: Interesting disk throughput performance problem

["Jakob Østergaard" <jakob@unthought.net>]

On Sat, Jul 21, 2001 at 11:33:13PM -0400, Jimmie Mayfield wrote:
> Hi.  I'm running into some disk throughput issues that I can't explain.
> Hopefully someone reading this can offer an explanation.
> 
> One of my machines is running 2.4.5 and has 2 hard drives: a 7200 rpm
> ATA100 Maxtor and a 5400 rpm ATA33 IBM.  Each drive is a master on its own
> controller (AMI CMD649 as found on the IWill KT266-R).  Both drives contain
> reiserfs 3.6x filesystems.  
> 
> By all local benchmarks, the 7200 rpm drive is the faster drive.  But this 
> doesn't seem to be the case for large files originating from remote clients.  
> Witness:
....
> So I tried the test locally:  with the file stored on the 5400rpm drive, 
> scp it to localhost and write it to the 7200rpm drive.  Results were a little 
> below 10MB/sec (CPU near 100% presumably due to encrypting/decrypting on 
> the fly).
> 
> Any ideas why the 7200rpm drive performs so poorly for remote clients but 
> performs wonderfully well when those same operations are performed locally?

This is a wild guess:

Try cat /proc/interrupts

Would the 7200 rpm drive controller happen to share an IRQ with your NIC ?

If so, something is horribly wrong since that shouldn't give that kind of
performance penalty.  But it's my best guess   :)

-- 
................................................................
:   jakob@unthought.net   : And I see the elder races,         :
:.........................: putrid forms of man                :
:   Jakob Østergaard      : See him rise and claim the earth,  :
:        OZ9ABN           : his downfall is at hand.           :
:.........................:............{Konkhra}...............: