Re: System Load analyze

On Wed, 28 Nov 2007, Peter Bauer wrote:

> PERC4E/DI DC ULTRA320 SCSI RAID, 256MB
> Its Debian sarge with kernel 2.4.26.050719-686 #1 SMP.

OK, so I'd expect you're using the megaraid2 driver.  That and kernel 
2.4.26 are a few years behind current at this point, and there have been 
plenty of performance improvements in Linux and that driver since then. 
Since you're asking about this before it's a serious problem and don't 
need an immediate fix, you may want to consider whether upgrading to a 
more modern 2.6 kernel is in your future; that change alone may resolve 
some of the possibly too high load you're having.  I doubt any 2.4 kernel 
is really getting the best from your fairly modern server hardsare.

Also, the PERC4E and similar Megaraid cards are known to be generally 
sluggish on write throughput compared with some of the competing products 
out there.  I don't know that I'd replace it though, as spending the same 
amount of money adding disks would probably be more useful.

There's actually a way to combine these two ideas and get an upgrade 
transition plan.  Buy a second disk, find a downtime window, install a 
newer Linux onto it and test.  If that works well switch to it.  If it 
doesn't you still have the original unmodified system around and you can 
at least split the disk load between the two drives.

> vmstat and iostat were running with 1 second intervals.

Good, that means the responses you've already gotten made the right 
assumptions.  There's some additional fun statistics you can collect with 
the Linux iostat, but sadly that needs a newer kernel as well.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD