Re: Interesting disk throughput performance problem

[Hans Reiser <reiser@namesys.com>]

I'm just guessing here, but is write caching active on one but not the other?

Hans


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:
> 
> My crude test involves scp'ing a 100MB file from another machine on my home
> network over 100bT ethernet.
> 
> 1)  scp to the 5400rpm drive:  roughly 10MB/sec.
> 2)  scp to the 7200rpm drive:  roughly 2MB/sec.
> 
> I've tried 'tail' and 'notail' mount options with no change (as expected since
> this is a single large file).  I suspect that the machine would become CPU-bound
> somewhere in the 20MB/sec range (see below for my reasoning).
> 
> I see the same sort of behavior using Samba though not nearly as
> pronounced (the 5400rpm drive is merely 2x as fast as the 7200rpm drive).
> 
> Okay.  Since the test involved 2 separate drives with different geometries,
> I figured this might be due to physical block location.  Perhaps the file
> is getting allocated to the fastest cylinders on the 5400 rpm drive and
> the slowest cylinders on the 7200 rpm drive.  Or it could be a fragmentation
> issue.
> 
> 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?
> 
> Jimmie
> 
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