I have a server running Slackware64 ver. 13.
The SATA controller on the motherboard is only SATA I.
The 2 hard drives are 500GB SATA II Western Digital ABYS.

I setup /dev/md0 (in raid 1) on a 100 gig. partition using default settings with ext4 file system. When I do dd write and read testing using 4k, 8k, 16k byte-sizes, I'm only getting a write speed of 22-25 MB/sec. and read speed of 70-72 MB/sec. Not very impressive.

Example tests --

time sh -c "dd if=/dev/zero of=bigfile bs=4k count=_blocks_ && sync"

time dd if=bigfile of=/dev/null bs=4k

I've created 6 additional /dev/md* raid 1 arrays to experiment with and I'd like to get some advice about tuning ext4 on 2 raid1 devices:
block-size
stride
fragment-size
journaling levels - journal, ordered, writeback

Your thoughts and comments are greatly appreciated.

I should add the environmental usage is probably 75% read and 25% write. 90% percent of file reading/writing is done on files of less than 1 meg.; however, I make .tar archives for storage and move them from partition to partition, and ultimately to other servers for storage. Those .tar files range from 15 - 30 gigs.

Latest testing showing very slow write speeds:

root@b1:/mnt/arc_sat# time sh -c "dd if=/dev/zero of=/mnt/arc_wed/bigfile bs=4k count=1000000 && sync"
1000000+0 records in
1000000+0 records out
4096000000 bytes (4.1 GB) copied, 383.042 s, 10.7 MB/s

real 6m33.257s
user 0m0.250s
sys 0m18.345s
root@b1:/mnt/arc_sat# time dd if=/mnt/arc_wed/bigfile of=/dev/null bs=4k
1000000+0 records in
1000000+0 records out
4096000000 bytes (4.1 GB) copied, 58.4375 s, 70.1 MB/s

real 0m58.479s
user 0m0.142s
sys 0m6.467s

- - - - - - - - - - - - - - - - - - -
Here's the dumpe2fs and mdadm details of the 2-drive raid1 array:

root@b1:/mnt/arc_sat# dumpe2fs -h /dev/md4
dumpe2fs 1.41.8 (11-July-2009)
Filesystem volume name: <none>
Last mounted on: <not available>
Filesystem UUID: 7a679b0d-ddf4-4591-9b06-5b79236114ae
Filesystem magic number: 0xEF53
Filesystem revision #: 1 (dynamic)
Filesystem features: has_journal ext_attr resize_inode dir_index filetype needs_recovery sparse_super large_file
Filesystem flags: signed_directory_hash
Default mount options: journal_data
Filesystem state: clean
Errors behavior: Continue
Filesystem OS type: Linux
Inode count: 3940352
Block count: 15731616
Reserved block count: 157316
Free blocks: 14437272
Free inodes: 3940340
First block: 0
Block size: 4096
Fragment size: 4096
Reserved GDT blocks: 1020
Blocks per group: 32768
Fragments per group: 32768
Inodes per group: 8192
Inode blocks per group: 512
Filesystem created: Sat Jun 26 18:57:10 2010
Last mount time: Sat Jun 26 21:12:52 2010
Last write time: Sat Jun 26 21:12:52 2010
Mount count: 1
Maximum mount count: 50
Last checked: Sat Jun 26 18:57:10 2010
Check interval: 15552000 (6 months)
Next check after: Thu Dec 23 17:57:10 2010
Reserved blocks uid: 0 (user root)
Reserved blocks gid: 0 (group root)
First inode: 11
Inode size: 256
Required extra isize: 28
Desired extra isize: 28
Journal inode: 8
Default directory hash: half_md4
Directory Hash Seed: 7583ae16-4e52-495e-b7d3-c8226c367d96
Journal backup: inode blocks
Journal size: 128M

and

root@b1:/mnt/arc_sat# mdadm --detail /dev/md4
/dev/md4:
Version : 00.90.03
Creation Time : Sat Jun 26 15:04:23 2010
Raid Level : raid1
Array Size : 62926464 (60.01 GiB 64.44 GB)
Used Dev Size : 62926464 (60.01 GiB 64.44 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 4
Persistence : Superblock is persistent

Update Time : Sun Jun 27 02:16:48 2010
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

UUID : 412c14ca:8cfb89a3:7cdeb91c:0ba389e0
Events : 0.6

Number Major Minor RaidDevice State
0 8 6 0 active sync /dev/sda6
1 8 22 1 active sync /dev/sdb6

Does anyone have any suggestions on how to get better performance out of this older SATA I onboard controller?
This is the mainboard:
Arima HDAMA 40-CMO120-A800
http://www.arimacorp.com/ViewProduct.asp?View=86

I've disabled the onboard Silicon Image Sil3114 raid controller.
The raid1 array is mdadm software raid.

I unmounted all 6 raid1 arrays and reinstalled the ext4 filesystem using the following command:

mke2fs -t ext4 -b 4096 -O has_journal,dir_index /dev/md*

Write speeds have improved to 25MB/sec.
Read speeds are about the same as before 65-70MB/sec.

It's good to see the write speed improvement; however, it still seems much slower than it should be. Seems like these hard drives should be able to sustain 50MB/sec. writes.

I'm marking this thread solved.
I've tested ext4 with settings of: journal_data, journal_data_writeback, and journal_ordered.
I've increased commit="seconds" to 30, 60, 90, 120
I've tried "noatime" parameter.
And several different mixtures of all three above.

I'm getting the same performance on this hardware: 70MB/s. Read & 24-25MB/s. Write.

I'm speculating, but I'll posit the largest factor affecting performance is the older SATA 1 onboard controller working with Raid1. The cpu(s) are 2 dual-core opterons running at 2.2Ghz with 4 gigs. of ECC RAM, so I don't think there's a performance problem there. When I tested single hard-drive performance on the WD 500Gig. ABYS drives, I was getting 50 MB/s. Writes and 75-85 MB/s. Reads.