[ILUG] Disk throughput on current generation server hardware

[Niall O Broin]

I have a few HP DL380 servers, with 2 x quad core 2.66 GHz Xeons, 12  
GB RAM, and 8 x 300 GB 10K RPM SAS disks in a RAID6 array on a Smart  
Array P410i controller.  The servers were originally deployed with  
SLES10SP2 where they proved very unreliable - sustained disk I/O would  
kill them.

After spending a long time with HP on support tickets, where we were  
told to do such inane things as update the ILO firmware (because of  
course that's intimately involved in disk I/O) we eventually installed  
SLES10SP3 on one of them and SLES11 on another, and they seem to have  
ceased dying, which is of course A Good Thing. However, the disk  
throughput is now a bit disappointing. The simple test we were using  
to exercise the disks was to run in a loop the following:

dd if=/dev/cciss/c0d0p4 of=/opt/dd_test count=20000 bs=1M

I know we could do much 'better' tests with bonnie or some such but  
our initial objective was to provoke the failures which we were seeing  
in normal use, and which we suspected were disk I/O related, and the  
dd test did that just nicely. It gave us a means of relatively quickly  
seeing if HP's latest suggestion was of any use.

The dd test gave the following approximate throughput figures:


OS release	Kernel version		Throughput

SLES10SP2	2.6.16.60-0.21-smp	100 MB/s
SLES10SP3	2.6.16.60-0.54.5-smp 	50 MB/s
SLES11		2.6.27.19-5-default	30 MB/s


SLES10SP2 is of course the outright winner here - unfortunately that  
speed came at the cost of stability.

The reason for this post is to get people's views as to what kind of  
throughput I should reasonably be able to expect on that class of  
hardware.


Niall