Outline for today Topic: MEMStore paper Administrative: No class on Wednesday!

Outline for today

• Topic: MEMStore paper• Administrative:

• No class on Wednesday!

MEMS-based Storage

David Nagle, Greg, Ganger, Steve Schlosser, and John Griffin

http://www.chips.ece.cmu.edu/

David Nagle December, 2000http://www.chips.ece.cmu.edu

What if a “disk drive” could …• Storage 10 Gbytes of data

• In the size of a penny• Deliver 100 MB – 1 GB/sec bandwidth• Deliver access times 10X faster than today’s drives• Consume ~100X less power than low-power disk drives• Integrate storage, RAM, and processing on the same die

• The drive is the computer• Cost less than $10


How do you put a “Disk Drive” on a chip?

• Build storage using MEMS• MEMS are

MicroElectricMechanicalSystems• Physical sensor and actuator systems

with features measured in microns

• Built using process technologies similar to current CMOS fabs

• Enable co-location of nonvolatile storage, RAM and processing on same physical chip


Example

• The world's smallest guitar is 10 micrometers long –• about the size of a single cell -- with six strings each about 50 nanometers, or 100 atoms, wide. Made by

Cornell University researchers from crystalline silicon, it demonstrates a new technology for a new generation of electromechanical devices. Photo by D. Carr and H. Craighead, Cornell.The above image (508 x 327 pixels) is the digital image created by the electron microscope, and is the highest-resolution version available.


Applications of MEMS

• Sensors• accelerometers• gyroscopes

• Actuators• micromirror arrays for LCD projectors• heads for inkjet printers• optical switches• microfluidic pumps for delivering medicine


MEMS-based Storage• On-chip Magnetic Storage - using MEMS for media positioning

Read/Writetips

Read/Writetips

MagneticMedia

MagneticMedia

ActuatorsActuators


MEMS-based Storage

Read/writetips

Read/writetips

MediaMedia

Bits storedunderneath

each tip

Bits storedunderneath

each tipside view


MEMS-based Storage

1 mprobe tip

100 m

group of six tips

• Read/write probe tips


MEMS-based StorageMedia Sled

X

Y


MEMS-based Storage

Springs Springs

SpringsSprings

X

Y


MEMS-based Storage

Anchors attachthe springs to

the chip.

Anchors attachthe springs to

the chip.

Anchor Anchor

AnchorAnchor

X

Y


MEMS-based Storage

Sled is freeto move

Sled is freeto move

X

Y


MEMS-based Storage

Springs pullsled toward

center


center

X

Y


MEMS-based Storage

X

Y


center


center


MEMS-based Storage

Actuators pullsled in bothdimensions


Actuator

Actuator

Actuator

Actuator

X

Y


MEMS-based Storage



X

Y


MEMS-based Storage

Probe tipsare fixed

Probe tipsare fixed

Probe tip

Probe tip

X

Y


MEMS-based Storage

X

Y

Probe tipsare fixed

Probe tipsare fixed


MEMS-based Storage

X

Y

Sled onlymoves overthe area of asingle square

Sled onlymoves overthe area of asingle square

One probe tipper square

One probe tipper square

Each tipaccesses dataat the same

relative position

Each tipaccesses dataat the same

relative position


Why Use MEMS-based Storage?

• Cost !• 10X cheaper than RAM• Lower cost-entry point than disk

• $10-$30 for ~10 Gbytes• New product niches• Can be merged with DRAM & CPU(s)

• Example Applications:• “throw-away” sensors / data logging

systems infrastructure monitoring; e.g., bridge monitors, concrete pours, smart highways, condition-based maintenance, security systems, low-cost speaker-independent continuous speech recognition, etc.

• Ubiquitous use in everyday world … every appliance will be smart, store information, and communicate

0.01 GB

0.1 GB

1 GB

10 GB

100 GB

$1 $10 $100 $1000

CACHE RAM

DRAM

HARDDISK

Entry Cost

Capacity @ Entry Cost

MEMS


Why Not EEPROM?• We have computers on a chip now - Embedded computers

• Billions of embedded CPUs sold today • How are HI2PS2 different today’s “embedded computer”?

• Currently nonvolatile memory is EEPROM (FLASH memory)• MEMS >> increase in nonvolatile mass memory (many GB)

• EEPROM* Feature Size Scaling vs. Time: 1997 1999 2001 2003 2006

2009

NOR Cell Area (um2) 0.6 0.3 0.22 0.15 0.080.04

(density MB/cm2) 16 32 44 64 120240

EEPROM cost $/MB $4 $2 $1.5 $1$0.53 $0.27 (Best Case - no increase in fab cost / cm2)

• Taking EEPROM prices as $0.27/MB --> 10GB = $2,700• For IC-Based Storage in 2009 we predict cost ~$25 / 10GB

• > 100X better than EEPROM* From Semiconductor Industries Association (SIA) Roadmap 1997


Why Use MEMS-based Storage?

• 10 GByte/cm2 = 65 GB/in2 density (100x CD-ROM)• 30 nm x 30 nm bit size• Example Applications:

• Space / satellite use - store data when not in line of site act as packet buffer for communications satellites, etc.

• Human portable applications - e.g., medical implants, super PDA• Law enforcement / monitoring devices / security surveillance

100,000

Occupiedvolume [cm3]

0.1 1 10 100 1000 10,0000.1

10

100

1000

10,000

Storage Capacity [GByte]

3.5” Disk Drive

Flash memory, 0.4 µm2 cell

Chip-sized data storage@ 10 GByte/cm21

• Volume !


Why Use MEMS-based Storage?• Lower Data Latency !

• Conventional disk drives: worst-case rotational latency 5-11ms• IC-Based Mass Storage: depends on design - 100’s of s possible• Example Applications

• Transaction-processing storage, Non-volatile storage hierarchies, network-buffers

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


ManagingMEMS-based Storage

• MEMS Data Layout

Sector is8 data bytes +ECC + servo

Sector is8 data bytes +ECC + servo

Media areadivided into“regions”

Media areadivided into“regions”

2500

2500

Data storedin “sectors”of ~100 bits

Data storedin “sectors”of ~100 bits


Data layout

• Optimized for:• Sequential access• Local access

1 2 3 2500…

• Serpentine layout


Read-modify-writeexample

Read-modify-writeexample

1 2 3 2500…


Fast Read-Modify-Write

• Disks must wait an entire disk rotation to perform a read-modify-write • MEMS devices can quickly turn around and write (or rewrite

a sector)• Example: Read-modify-write of 8 sectors (4KBytes) in msecs

Atlas 10K MEMS

Read 0.14 0.13

Reposition 5.98 0.07

Write 0.14 0.13

Total 6.26 0.33


X-dimension Settling Time• Consider a simple seek

...

...

...

...

Sweep area of one probe tip

Oscillations in XOscillations in X

Oscillations in YOscillations in Y

Why do we onlycare about theX dimension?



X-dimension Settling Time

Oscillations in Xlead to off-track

interference!

Oscillations in Xlead to off-track

interference!

In Y, the oscillationsappear as slight

variations in velocity,which can be

tolerated.

In Y, the oscillationsappear as slight

variations in velocity,which can be

tolerated.

Sled is movingin Y

Sled is movingin Y




Seek Time from Center

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-1000 -500 0 500 1000

Seek

tim

e (

ms)

X displacement (bits)


Seek Time from Center

00.20.40.60.8

SeekTime(ms)

X500

0-500

-1000

YDisplacement

-5000

500Displacement1000


The Effect of Settle Time

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-1000 -500 0 500 1000

Seek

tim

e (

ms)

Displacement (bits)

Seek time in YSeek time in Y

Seek time in XSeek time in X

without settling constantwith settling constant


Seek Time Without Settle

00.20.40.6

SeekTime(ms)

X500

0-500

-1000

YDisplacement

-5000

500Displacement1000


Access data and then turn around

and access same data



Turn-around






Turn-around

Turning “Turn-around”,

No data is accessed


No data is accessed






Turn-around






Turn-around


No data is accessed


No data is accessed


OS view of MEMS-based storage

• High-level MEMS characteristics:• Long positioning times• High streaming rate

• Logical block interface works well• Opportunities for device optimization, but convoluted tricks

not necessary

FAST 2004 Paper• Specificity test – are the benefits of a policy or role MEMS-

specific?• If fails (performance same when compared to fast disk),

MEMStore considered just like a fast disk wrt this role or policy

• Merit test • If MEMS-specific, is it worth it (>10% improvement)?

• Standard Storage Interface (interoperability)• Linear array of logical blocks (512 bytes)• Exact mapping of LBN to physical media is hidden

• Contract for the Standard Interface (performance model)• Sequential access is best• Access to nearby LBN is more efficient that distant• Ranges of LBN are interchangeable

• Good qualitative arguments for MEMStores to be block-oriented and the contract stays valid


Request scheduling

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Distance

See

k ti

me

(ms)

0-MAX MAX


Request scheduling

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Distance

See

k ti

me

(ms)

0-MAX MAX

Seek time in XSeek time in X

Seek time in YSeek time in Y

Substituting/Migrating in Disk Array


MEMS scheduling

0

20

40

60

80

100

100 500 900 1300 1700 2100

Mean arrival rate (Hz)

Ave

rag

e re

spo

nse

tim

e (m

s) FCFS

Saturation pointSaturation point

(first come, first served)


MEMS scheduling

0

20

40

60

80

100

100 500 900 1300 1700 2100


Ave

rag

e re

spo

nse

tim

e (m

s) FCFS

SSTF

(shortest “seek time” first)


MEMS scheduling

0

20

40

60

80

100

100 500 900 1300 1700 2100


Ave

rag

e re

spo

nse

tim

e (m

s) FCFS

SSTF

SPTF

(shortest positioning time)


Disk scheduling

0

20

40

60

80

100

10 50 90 130 170 210


Ave

rage

res

pons

e tim

e (m

s) FCFS

SSTF

SPTF

X-axis shiftX-axis shift

Curves saturatein same order,relative position

Curves saturatein same order,relative position

FAST 2004 Scheduling Results

SDF isShortestDistanceFirst


Data layout

• Basically as for disks• Sequential access >>> not sequential• Local access > not local

• Some interesting differences• File size vs. physical location


Small requests

0.42 ms/movein this subregion

0.37 ms/movein this subregion


Large requests: 256KB

• Transfer time dominates positioning time

0

1

2

3

4

Distance (in X)

Ave

rag

e re

spo

nse

tim

e (m

s)

0 MAX

Short seekShort seek Long seekLong seek


Bipartite layout

Metadata orsmall objects

Large/streaming objects

FAST 2004: MEMStore Specific Features• Tip – subset parallelism• 2D data structures• Quick turnarounds

(read-modify-write operations)

• Device scan

2D Data Structure Accesses


Failure Management

• MEMS devices will have internal failures• Tips will break during fabrication/assembly … and during

use• Media can wear

• With multiple tips, data and ECC can be striped across the tips• ECC can be both horizontal and vertical• On tip or tip-media failure, ECC prevents data loss• Could then use spares to regain original level of reliability


Failure Management



Probe Tip


Failure Management



Probe Tip

Spare Tip

Spare Tip


MEMS in Computer Systems

• MEMS-based storage device simulator• Uses first-order mechanics

• Integrated into DiskSim• Models events, busses, cache• Compare against simulated disks

• SimOS-Alpha• Full machine simulator with DiskSim as storage subsystem


Random Workload - 15X Speedup

10,000 small random requests, 67% reads,exponentially sized with mean 4KB.

0

2

4

6

8

10

12

1999 Disk 2003 Disk MEMS

Storage Device Type

Ave

rage

Acc

ess

Tim

e (m

s)



Random Workload - 15X Speedup


0

2

4

6

8

10

12


Storage Device Type

Ave

rage

Acc

ess

Tim

e (m

s)

MEMS has smallpositioning variability

MEMS has smallpositioning variability


PostMark - 5X Speedup

0

100

200

300

400

500

600

700

800


Storage Device Type

Ove

rall

Run

time

(s)


MEMS-based Storage as Disk Cache

File SystemFile System

Disk

MEMSCache

MEMSCache

HP Cello tracehas 8 disks

10.4GB total capacity

HP Cello tracehas 8 disks

10.4GB total capacity

1999 Disk(Quantum Atlas 10K)

9 GB

1999 Disk(Quantum Atlas 10K)

9 GB

Baseline MEMS3 GB

Baseline MEMS3 GB


Baseline Configuration


DiskDisk Disk Disk


Disk Cache Configuration


MEMSMEMSMEMSMEMS MEMSMEMS MEMSMEMS


Disk Cache Configuration


Disk

MEMSCache

MEMSCache

Disk

MEMSCache

MEMSCache

Disk

MEMSCache

MEMSCache

Disk

MEMSCache

MEMSCache


MEMS-based Storage As a Disk Cache

02468

10121416

1999 Disk MEMS only 1999 Disk +MEMS Cache

Storage Device Type

Ave

rage

Acc

ess

Tim

e (m

s)


File System-managed Layout

• File system could allocate data directly

MEMSMEMS Disk

File systemFile system

• Metadata• Small files• Paging

• Large, streaming files


Perf Idle Fast

Idle Low power Idle Standby

Active

Low-power Disk Drives

• IBM Travelstar 8GS

Time (s)

Pow

er (

W)

0

1

2

3

0 5 10

Command stream ends

40 ms40 ms

2 s2 s400 ms400 ms


MEMS-based Storage

• 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

0.5 ms0.5 ms

Active

Time (s)

Pow

er (

W)

0

1

0 5 10

Standby(not to scale)

Standby(not to scale)

• Fast transition from standby


PostMark

0

500

1000

1500

2000

2500

3000

3500

Travelstar MEMS

Storage Device Type

Ene

rgy

(Jou

les)

3111

58


PostMark

0

500

1000

1500

2000

2500

3000

3500

Travelstar MEMS

Storage Device Type

Ene

rgy

(Jou

les)

Performance IdlePerformance Idle

ActiveActive

ActiveActive


Netscape

0

1000

2000

3000

4000

5000

6000

7000

Travelstar MEMS

Storage Device Type

Ene

rgy

(Jou

les)

6097

349


Netscape

0

1000

2000

3000

4000

5000

6000

7000

Travelstar MEMS

Storage Device Type

Ene

rgy

(Jou

les)

Lots of transitionsLots of transitions

Largely idleLargely idle

ActiveActive


Future of MEMS-based Storage

• Perfect for portable devices• Size, capacity, power


MEMS-based Storage Is On the Way

• Interesting new storage technology• Gigabytes of non-volatile data in a single IC• Sub-millisecond average access time• Low power

• Can fill various roles• Augment memory hierarchy• Portable devices• Archival storage• Active storage devices


MEMS-based Storage at CMU

lcs.web.cmu.edu/research/[email protected]

Outline for today Topic: MEMStore paper Administrative: No class on Wednesday!

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