uname -r
2.6.27.12-readahead

scheduler: deadline
/dev/sda - RA 2048
/dev/sdb - RA 2048
/dev/md0 - RA 2048
/dev/raid/1st - RA 2048
/dev/raid/3rd - RA 2048

linux-4dtq:/ # echo > /sys/kernel/debug/readahead/stats
linux-4dtq:/.kernels/scst-kernel-3 # cat /sys/kernel/debug/readahead/stats
pattern         count sync_count  eof_count       size async_size     actual
none                0          0          0          0          0          0
initial0            0          0          0          0          0          0
initial             0          0          0          0          0          0
subsequent          0          0          0          0          0          0
marker              0          0          0          0          0          0
trail               0          0          0          0          0          0
oversize            0          0          0          0          0          0
reverse             0          0          0          0          0          0
stride              0          0          0          0          0          0
thrash              0          0          0          0          0          0
mmap                0          0          0          0          0          0
fadvise             1          1          1          0          0          0
random              0          0          0          0          0          0
all                 1          1          1          0          0          0


On initiator run benchmark:
dd if=/dev/sdb of=/dev/null bs=64K count=8000
dd if=/dev/sdc of=/dev/null bs=64K count=8000


linux-4dtq:/.kernels/scst-kernel-3 # cat /sys/kernel/debug/readahead/stats
pattern         count sync_count  eof_count       size async_size     actual
none                0          0          0          0          0          0
initial0            2          2          1          4          3          2
initial             1          1          0          4          3          4
subsequent        301          0          0        420        253        253
marker            705          0          0        255        255        255
trail               0          0          0          0          0          0
oversize            0          0          0          0          0          0
reverse             0          0          0          0          0          0
stride              0          0          0          0          0          0
thrash              0          0          0          0          0          0
mmap                2          2          2         32          0         12
fadvise             2          2          2          0          0          2
random              0          0          0          0          0          0
all              1013          7          5        303        253        253



linux-4dtq:/ # echo 1 > /sys/kernel/debug/readahead/trace_enable


NOW ON INITIATOR
dd if=/dev/sdc of=/dev/null bs=64K count=8000
dd if=/dev/sdb of=/dev/null bs=64K count=8000

echo 0 > /sys/kernel/debug/readahead/trace_enable
dmesg

