PE 840 very slow

[Patrick Michael Kane]

* Richard DeSimine (rdesimine at comcast.net) [071203 20:48]:
> (this is my 1st post to this forum)
> 
> I got new PowerEdge 840 loaded with RedHat Enterprise 5.1, 4GB ram and a
> 2.4ghz QuadCore processor. 
> 
> >uname -a
> Linux <hostname> 2.6.18-53.1.4.el5 #1 SMP Wed Nov 14 10:37:27 EST 2007
> x86_64 x86_64 x86_64 GNU/Linux
> 
> It has a SAS5/IR (SAS) card and 2 250GB ATA drives configured as RAID 1.
> 
> Disk I/O is slow. Very SLOW. Comparing it to the PowerEdge 700 which I
> am upgrading, which is a single CPU single drive 2.3ghz Pentium, the
> disk writes take about 8x longer on the new 840. Furthermore, when any
> process is performing I/O, no other process can get access to the disk,
> and all process effectively are hung.
> 
> Is anyone else experiencing this problem?

Rich:

We had a similar problem that was solved by turning on the
controller's write cache.

You can't do this using OMSA, as far as I can tell, but you can do it
using lsiutil, which is buried inside of the Dell driver tarfile.

You can find details here:

  http://kerneltrap.org/mailarchive/openbsd-misc/2007/7/15/152340

This solved the problem for our server.

We're not particularly concerned about losing data in the case of
power failure, though.  If that's a concern for you, you should
consider using another controller, as the SAS/5IR does not have a
battery backup option.

Best,
-- 
Patrick Michael Kane
<modus-dell at pr.es.to>