{upstream} Raid10,o2 only reads from a single disk

installed 8.04 64bit server from CD.
installed sysstat package.
mdadm --create /dev/md3 --level=10 --raid-devices=2 --chunk=512 --layout=o2 /dev/sdh1 /dev/sdd1

Det ser ud til at der kun læses fra een (1) disk i et RAID10,o2 array med 2 diske.
Eg:
 /dev/md3 = Raid10,o2 on 2 disks sdd1 and sdh1:

dd if=16GigaByte-FileOnRaidArray of=/dev/null
33554432+0 records in
33554432+0 records out
17179869184 bytes (17 GB) copied, 353,121 s, 48,7 MB/s

iostat during dd :
avg-cpu: %user %nice %system %iowait %steal %idle
           0,67 0,00 10,07 39,87 0,00 49,40

Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
sdd 0,00 0,00 0,00 0 0
sdi 145,53 48,06 0,00 720 0
md3 11944,53 48,04 0,00 720 0

At no time is there read from /dev/sdd.
Repeating "dd if=16GigaByteFileOnRaidArray of=/dev/null"
Might result in iostat reporting:

avg-cpu: %user %nice %system %iowait %steal %idle
           0,47 0,00 9,27 40,87 0,00 49,40

Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
sdd 120,67 39,16 0,00 587 0
sdi 0,00 0,00 0,00 0 0
md3 9751,67 39,21 0,00 588 0

At no time is there read from /dev/sdi.

--- 2nd. test
Booting on intrepid 64bit live-cd (desktop)
mdadm --assemble --scan /dev/md3
apt-get sysstat
dd if=16GigaByte-FileOnRaidArray of=/dev/null

And iostat reports that there is read from both disks.
And throughput seemed higher.

--- 3rd. test
Booting on Hardy 8.02-2 64bit live-cd (desktop)
mdadm --assemble --scan /dev/md3
apt-get sysstat
dd if=16GigaByte-FileOnRaidArray of=/dev/null

And iostat reports that there is only read from ONE disk.

Forcing sysstat to ver.8.1.2-2 from intrepid.
rerunning test
iostat _still_ reports that there is only read from ONE disk.

- Should be easily reproduceable.

/Kenn