Disk I/O as a bottleneck?

[Eli Billauer]

I would suggest making the check I mention in my own blog, in particular 
if you're running an old kernel. There has been a bug in the way the 
kernel handles heavy disk loads.


http://billauer.co.il/blog/2010/10/disk-io-scheduler-load-dd-freeze-stall-hang/


Omer Zak wrote:

> I have a PC with powerful processor, lots of RAM and SATA hard disk.
> Nevertheless I noticed that sometimes applications (evolution E-mail
> software and Firefox[iceweasel] Web browser) have the sluggish feel of a
> busy system (command line response time remains crisp, however, because
> the processor is 4x2 core one [4 cores, each multithreads as 2]).
>
> I run the gnome-system-monitor all the time.
>
> I notice that even when those applications feel sluggish, only one or at
> most two CPUs have high utilization, and there is plenty of free RAM (no
> swap space is used at all).
>
> Disk I/O is not monitored by gnome-system-monitor.
> So I suspect that the system is slowed down by disk I/O.  I would like
> to eliminate it as a possible cause for the applications' sluggish feel.
>
> I ran smartctl tests on the hard disk, and they gave it clean bill of
> health.  Therefore I/O error recovery should not be the reason for
> performance degradation.
>
> I am asking Collective Wisdom for advice about how to do:
> 1. Monitoring disk I/O load (counting I/O requests is not sufficient, as
> each request takes different time to complete due for example to disk
> head seeks or platter rotation time).
> 2. Disk scheduler fine-tuning possibilities to optimize disk I/O
> handling.
> 3. If smartctl is not sufficient to ensure that no I/O error overhead is
> incurred, how to better assess the hard disk's health?
>
> Thanks,
> --- Omer
>
>   


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Web: http://www.billauer.co.il