[wellylug] High load averages but no apparent cause

Daniel Reurich daniel at centurion.net.nz
Tue Mar 23 09:20:14 NZDT 2010


On Tue, 2010-03-23 at 08:50 +1300, David Harrison wrote:
> Thanks Daniel that switch for vmstat is very handy and I'd completely
> missed the io wait value in top.
> Googling based on your comments also brought up this page which is
> very handy:
> http://strugglers.net/wiki/Linux_performance_tuning
> 
> 
> The problem is certainly is looking like an intermittent I/O issue.
> 
Probably caused by a disk issue - seriously.  I have seen this before.
> 
> Has anyone experience with the performance boost of a dedicated PCI-X
> SATA controller for software RAID?

> 
> The server in question is a bog-standard HP ML110.
> It isn't up to their needs, but it was a recent purchase by the
> previous IT guys, so I'm afraid it is staying.
> 
I don't think it should be an issue.
> 
> For practical reasons I want to keep the software RAID-5 (3x1TB
> drives), but would putting some (or all) of these disks onto a
> dedicated controller alleviate the I/O issue?
> 
I'd say it would provide none to minimal gain given your load stats if
you are using software raid, and a small gain if you get hardware raid.
> 
> i.e. Is it worth recommending a $400 PCI-X SATA controller for the
> box, or is that money better left on the table for a new server
> (ML310/330) in twelve months time?
> (My concern being that the card goes in and the problem remains the
> same.)

Save the money unless you can be sure it's the built in controller (I
doubt it is).

I think your next port of call is to d a SMART check on your drives.
Install smartmontools and do a smartctl -son /dev/sdX for each drive,
and report that back if you don't understand the results.

Regards,
	Daniel.






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