MEMS Based Mass Storage Systems

What is MEMS?

• (M)icro(E)lectric(M)echanical(S)ystems• Consist of mech µ(structures, sensors,

actuators), electronics, integrated onto same chip

• Transducer = Sensor / Actuator• Smart sensors• Cheap• Examples

Fender?

•The world's smallest guitar is 10 micrometers long –

Made by Cornell University researchers from crystalline silicon

Example

Why use MEMS?

• Cost

• Examples

0.01 GB

0.1 GB

1 GB

10 GB

100 GB

$1 $10 $100 $1000

CACHE RAM

DRAM

HARDDISK

Entry Cost

MEMS

Capacity @ Entry Cost

Why use MEMS?(cont.)

• Volume

• Examples

100,000

Occupiedvolume [cm3]

0.1 1 10 100 1000 10,0000.1

10

100

1000

10,0003.5” Disk Drive

Flash memory, 0.4 µm2 cell

Chip-sized data storage@ 10 GByte/cm21

Storage Capacity [GByte]

Why use MEMS?(cont.)

• Lower data latency

• Why not EEPROM?

Worst-CaseAccessTime

(RotationalLatency)

Cost $ / GB

$1 / GB

$3 / GB

$10 / GB

$30 / GB

$100 / GB

10ns 1µs 100µs 10ms

DRAM

HARD DISK

Prediction2008

$300 / GBEEPROM (Flash)

MEMS

Storage Device Design

• 2 proposed models– Cantilever– “Moving media”

“Moving Media”

Read/Writetips

Read/Writetips

MagneticMedia

MagneticMedia

ActuatorsActuators

“Moving Media” Read/writetips

Read/writetips

MediaMedia

Bits storedunderneath

each tip

Bits storedunderneath

each tipside view

Logistics

• Area = 1 cm2

• 10,000 probe tips• Bit cell of 0.0025-0.0009 µm2

4 – 11 GB

• Advantages / disadvantages

Data Layout

• Cylinders• Tracks• Sectors• Logical block

Device Performance

• timeservice=time

seek+latencyrotate+timetransfer

• MEMS

– timeservice=time seek +timetransfer

time seek,acceleration, turnaround time, settling time

Physical Characteristics

• Bit Size• Access Velocity• Sled acceleration• Spring stiffness• Number of sleds• Number of active tips• Error rates

Performance Characteristics

• Seek time• Settle time• Turnaround time• Peak bandwidth• Capacity• Power• Reliability

Example

• Fast read-modify-write• No rotational latency

Atlas 10K MEMSRead 0.14 0.13Reposition 5.98 0.07Write 0.14 0.13Total 6.26 0.33

Seek Time From Center

00.20.40.60.8

SeekTime(ms)

X500

0-500

-1000

YDisplacement

-5000

500Displacement1000

Sustained Data Rate

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

0.20 1.00 1.80 2.60 3.40

Per-tip Data Rate (Mbits/sec)

Sus

tain

ed D

ata

Rat

e (M

bits

/sec

) 1.6 Mbits / sec * 1280 tips = 2048 Mbits / sec

Sustained Data Rate

0.00

0.50

1.00

1.50

2.00

2.50

0.20 1.00 1.80 2.60 3.40 4.20 5.00

Per-tip Data Rate (Mbits/sec)

Sus

tain

ed D

ata

Rat

e (M

b/se

c)Baseline Decreased Bit Size Doubled Actuator Force

Failure Management

• MEMS devices will have internal failures– Tips will break during

fabrication/assembly, use– Media can wear

ECC can be both horizontal and verticalCould then use spares to regain original

level of reliability

Performance Models

• Generation 1• Generation 2• Generation 3• Reference disk – Atlas 10k• Super disk

Random Workload - Microbenchmark

0

2

4

6

8

10

12

1999 Disk 2003 Disk MEMS

Storage Device Type

Ave

rage

Acc

ess

Tim

e (m

s)

Postmark

0

100

200

300

400

500

600

700

800

1999 Disk 2003 Disk MEMS

Storage Device Type

Ove

rall

Run

time

(s)

Power Utilization

• Lower operating power– 100 mW for sled positioning– 1 mW per active tip– For 1000 active tips, total power is 1.1 watt– 50 mW standby mode

• Fast transition from standby – 0.5 ms

Future Potential

• Definite advantages• Portable applications• New low-cost entry point• Archival storage• Active storage devices• Throwaway devices• …

Problems?

• Very little has been implemented• Power consumption?• Heat – kinetic energy?• Reliability?• Sturdiness?• Any other alternatives?

Conclusions

• Potential to fill the RAM/Disk gap• Simulation results show

– reductions in I/O stall times– overall performance improvement

We’ll have to wait and see …