[CentOS] setting the device queue_depth

Hi,

Due to limitations of our Storage we need to set the device queue_depth to 4.
I did this with a script that basically does this: echo 4 > /sys/block/sdft/device/queue_depth.

But after a  few minutes it starts to grow until it reaches 32 again. What could cause that behavior?

Furthermore the system doesn' t load my qlogic options. I have set them to:
cat /etc/modprobe.d/qlogic.conf
                alias scsi_hostadapter1 qla2xxx
                options qla2xxx ql2xmaxqdepth=4

But the max queue depth is
cat /sys/module/qla2xxx/parameters/ql2xmaxqdepth
32

Any help would be appreciated.

Centos: CentOS release 6.3 (Final)
Storage: DDN 9900
Qlogic: 2560 (using distri firmware)


Cheers

Axel