[Disksim-users] Request coalescence

[YipKei Kwok]

Hi,

I am running Disksim w./ a trace workload.

Problem:
The amount of "Total Requests handled" by the disk is less than the
number of requests specified in the trace.

I suspect that is because of request coalescence/overlapping/combining.

disksim_ioqueue: Overlapping request scheme
-----------------------------------------------------------
- We have already set this parameter 0 so that overlapping requests
are treated as independent.

disksim_disk: Combine seq writes
-------------------------------------------
- The default value of our HP C3323 hard drive is 1. We experienced
_exactly_ the same problem even when we set it to 0.

I/O Driver Statistics
-------------------------
>From the statistics, both "IOdriver Overlaps combined" and "IOdriver
Read overlaps combined" are both 0. So, no requests are combined on
the I/O driver level.


Is there any other level of the I/O hierarchy could cause request
coalescence? Or, are there some other reasons, other than request
coalescence, which cause the problem that I am facing?

Thank you very much!

-Yipkei

P.S. Here is our experimental setup.
I/O trace-driven
raid 0 - 1 HP C3323A hard drive.
(Originally, there are 4 disks in the RAID. For simplicity, now we
only use 1. So, strictly speaking, it's not a RAID.
Number of processors = 1

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