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MEMSMODEL - version 1.0

Authors: Steve Schlosser and John Linwood Griffin - 1999 - 2005

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Summary
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The MEMSMODEL library provides a model of a MEMS-based storage device
described by Carley et al., and used in all of our systems research
over the past five years.  See http://www.pdl.cmu.edu/MEMS/ for a
summary of research and links to papers.  The model is configurable,
and is generally integrated into the DiskSim simulator.  The seek
model can be configured to be either our piecewise-linear model or a
more general solution described by Hong et al.  The library gathers a
wide variety of statistics on seek time, transfer time, energy used,
number of read/write tips engaged, etc.

Components/Features
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MEMSMODEL implements two different seek time calculation functions.
The first is a piecewise-linear calculation of seek time, described in
our SIGMETRICS paper from 2000.  The second is a general solution,
described by Bo Hong from UC Santa Cruz.  Experimentation has shown
that they give nearly identical results, although it has not been
rigorously tested across many workloads.  The seek functions are
implemented in mems_internals.c, mems_piecewise_seek.c, and
mems_hong_seek.c.  These are built into the mems_internals library,
and can be exercised independent of DiskSim.

MEMSMODEL is interfaced to DiskSim through mems_disksim.c and
mems_event.c.  The event loop in mems_event.c simulates requests being
executed by the MEMS model.  It has become pretty complicated over
time, but is based on the DiskSim simpledisk model
(disksim_simpledisk.c).

Many statistics are gathered while the simulation runs, and the
results are output in the DiskSim output file.

Overall seek time
X seek time
Y seek time
Initial turnaround time
Streaming turnaround time
Subtrack accesses
Tips per access
Number of spinups
Number of spindowns
Inactive time
Buffer accesses
Per-request energy
Total energy
Servicing energy
Startup energy
Idle energy
Inactive energy

An interesting feature of MEMSMODEL is its ability to access a batch
of requests using parallel read/write tips, even if those requests are
not to contiguous LBNs.  Batched requests are marked as such when
delivered to DiskSim, and MEMSMODEL will not begin executing them
until all of the requests in the batch have arrived.  If the requested
LBNs are at the same X/Y offset, then the model will access them with
parallel read/write tips, up to the number of tips that can be active
concurrently.  If there are not enough tips or if some of the LBNs are
at different X/Y offsets, then the simulator will access as many as it
can at once, and access those that remain in subsequent passes.

There is a simple re-use buffer, which is disabled in this version.
There is also rudimentary support for prefetching, which is also
disabled.

Configuration parameters
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Please see the user's manual for a description of each of the model's
parameters.

Using the library
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We have used the library in two different ways: as part of a
stand-alone program to study seek time dynamics of MEMS-based storage
devices and their dependence on various design parameters, and as part
of DiskSim to compare the performance of MEMS-based storage devices
and disk drives.  There is an example of how to generate basic seek
curves for each model in the tests/ directory.  The memsvalid script
in the disksim/valid directory will run some sample simulations
through DiskSim.  There are also sample configuration files in that
directory.

Known bugs
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Batches of parallel writes causes crashes - just use reads instead.

Buffer

Prefetching