[Disksim-users] IO Scheduling within Disk

[Prashant Saxena]

*

Hi DiskSim Users,

I am trying to simulate in-disk scheduling algorithm to determine the
effect of interleaving OS IO scheduling and in-disk IO scheduling
(scheduling within the disk). To test this feature I modified the
scheduling policy bit in diskspecs file and ran the simulation using ascii
trace file. However, I noticed that the “Overall I/O System Response time
average” along with other parameters remained unaffected from the choice of
scheduling algorithm used in disk. These parameters did change when I
changed the scheduling policy at the driver level, i.e, in the parv file.

Further Investigation:

I investigated further and found that “Max queue length” parameter for the
disk was set to 1 in diskspecs file. My intuition was that for any
scheduling to take place at disk level, it has to queue more than 1 IO
request. So I ran the test again after changing this value to x (any where
from 2 to 10000).  However, this created another problem. After changing
Max queue length,I found that disksim simulated only  36 IO requests (seen
from “Overall I/O System Total Requests handled” trace output) out of
nearly 10K IO requests in trace file. Note that disksim did not error out
while running this test, it simply processed less number of IOs. Also the
overall response time did not change with different choice of scheduling
algorithm at disk level.

I am not sure what is causing this problem. Simply put my intention is to
run disk-level scheduling and observe output characteristics. I would be
glad to share the parv and trace file if someone is interested in running
the test on their end.

Any help is appreciated.

Thanks,
Prashant Saxena *
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