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SubjectPROBLEM: Consistently slower 3ware RAID performance under 2.6.4
## Background:

I'm doing a lot of sequential read and write performance tests on my
3ware 7000-2 controller (RAID1 with 2xWD1200JB), because I'm getting
very poor write performance. This is a problem that I'm currently
working with 3ware to resolve, and they are working enthusiastically
with me to fix it.

Read test: time dd if=/dev/sda2 of=/dev/null bs=1024k count=1024
Write test: time dd if=/dev/zero of=/dev/sda2 bs=1024k count=1024

NOTE: /dev/sda2 is the swap partition which is NEAR the outer-most tracks.


## The new problem I discovered specific to Linux:

Regardless of the above-mentioned problem, I am noticing a very
significant performance drop between a 2.4 kernel and a 2.6 kernel.


## Performance with "2.4.25-gentoo":

The read test here takes 21.6 seconds which is about 47MB/sec. This is
a correct number, because I have measured the maximum read throughput
from each drive to be 47MB/sec.

The write test here takes 2 minutes, 2.5 seconds. This translates to
8.35MB/sec. This is what I'm working with 3ware to correct, but let's
call this the baseline write performance.


## Performance with "2.6.4-gentoo-r1":

The read test here takes 33.9 seconds. That's down to about 30MB/sec.

The write test here takes 2 minutes, 44.2 seconds. That is down to
6.2MB/sec.


## HELP?

How can I help kernel developers to diagnose this problem? What
information do I need to provide that is missing?

What is responsible for such a significant performance drop on LONG
sequential disk accesses?


## My computer:

Athlon 2800+
1GB RAM (Corsair 2700LL)
ABIT KD7 (KT400 chipset)


Thanks in advance for the help!

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