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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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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.
David Nagle December, 2000http://www.chips.ece.cmu.edu
Applications of MEMS
• Sensors• accelerometers• gyroscopes
• Actuators• micromirror arrays for LCD projectors• heads for inkjet printers• optical switches• microfluidic pumps for delivering medicine
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage• On-chip Magnetic Storage - using MEMS for media positioning
Read/Writetips
Read/Writetips
MagneticMedia
MagneticMedia
ActuatorsActuators
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
Read/writetips
Read/writetips
MediaMedia
Bits storedunderneath
each tip
Bits storedunderneath
each tipside view
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
1 mprobe tip
100 m
group of six tips
• Read/write probe tips
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
Springs Springs
SpringsSprings
X
Y
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
Anchors attachthe springs to
the chip.
Anchors attachthe springs to
the chip.
Anchor Anchor
AnchorAnchor
X
Y
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
Sled is freeto move
Sled is freeto move
X
Y
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
Sled is freeto move
Sled is freeto move
X
Y
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
Springs pullsled toward
center
Springs pullsled toward
center
X
Y
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
X
Y
Springs pullsled toward
center
Springs pullsled toward
center
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
Actuators pullsled in bothdimensions
Actuators pullsled in bothdimensions
Actuator
Actuator
Actuator
Actuator
X
Y
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
Actuators pullsled in bothdimensions
Actuators pullsled in bothdimensions
X
Y
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
Actuators pullsled in bothdimensions
Actuators pullsled in bothdimensions
X
Y
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
Actuators pullsled in bothdimensions
Actuators pullsled in bothdimensions
X
Y
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
Actuators pullsled in bothdimensions
Actuators pullsled in bothdimensions
X
Y
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
Probe tipsare fixed
Probe tipsare fixed
Probe tip
Probe tip
X
Y
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage
X
Y
Probe tipsare fixed
Probe tipsare fixed
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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 !
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
Data layout
• Optimized for:• Sequential access• Local access
1 2 3 2500…
• Serpentine layout
David Nagle December, 2000http://www.chips.ece.cmu.edu
Read-modify-writeexample
Read-modify-writeexample
1 2 3 2500…
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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?
Why do we onlycare about theX dimension?
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
Why do we onlycare about theX dimension?
Why do we onlycare about theX dimension?
David Nagle December, 2000http://www.chips.ece.cmu.edu
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)
David Nagle December, 2000http://www.chips.ece.cmu.edu
Seek Time from Center
00.20.40.60.8
SeekTime(ms)
X500
0-500
-1000
YDisplacement
-5000
500Displacement1000
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
Seek Time Without Settle
00.20.40.6
SeekTime(ms)
X500
0-500
-1000
YDisplacement
-5000
500Displacement1000
David Nagle December, 2000http://www.chips.ece.cmu.edu
Access data and then turn around
and access same data
Access data and then turn around
and access same data
Turn-around
David Nagle December, 2000http://www.chips.ece.cmu.edu
Access data and then turn around
and access same data
Access data and then turn around
and access same data
Turn-around
David Nagle December, 2000http://www.chips.ece.cmu.edu
Access data and then turn around
and access same data
Access data and then turn around
and access same data
Turn-around
David Nagle December, 2000http://www.chips.ece.cmu.edu
Access data and then turn around
and access same data
Access data and then turn around
and access same data
Turn-around
Turning “Turn-around”,
No data is accessed
Turning “Turn-around”,
No data is accessed
David Nagle December, 2000http://www.chips.ece.cmu.edu
Access data and then turn around
and access same data
Access data and then turn around
and access same data
Turn-around
David Nagle December, 2000http://www.chips.ece.cmu.edu
Access data and then turn around
and access same data
Access data and then turn around
and access same data
Turn-around
David Nagle December, 2000http://www.chips.ece.cmu.edu
Access data and then turn around
and access same data
Access data and then turn around
and access same data
Turn-around
Turning “Turn-around”,
No data is accessed
Turning “Turn-around”,
No data is accessed
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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)
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
SSTF
(shortest “seek time” first)
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
SSTF
SPTF
(shortest positioning time)
David Nagle December, 2000http://www.chips.ece.cmu.edu
Disk scheduling
0
20
40
60
80
100
10 50 90 130 170 210
Mean arrival rate (Hz)
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
Data layout
• Basically as for disks• Sequential access >>> not sequential• Local access > not local
• Some interesting differences• File size vs. physical location
David Nagle December, 2000http://www.chips.ece.cmu.edu
Small requests
0.42 ms/movein this subregion
0.37 ms/movein this subregion
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
Failure Management
• MEMS devices will have internal failures• Tips will break during fabrication/assembly … and during
use• Media can wear
Probe Tip
David Nagle December, 2000http://www.chips.ece.cmu.edu
Failure Management
• MEMS devices will have internal failures• Tips will break during fabrication/assembly … and during
use• Media can wear
Probe Tip
Spare Tip
Spare Tip
David Nagle December, 2000http://www.chips.ece.cmu.edu
Failure Management
• MEMS devices will have internal failures• Tips will break during fabrication/assembly … and during
use• Media can wear
Probe Tip
Spare Tip
Spare Tip
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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)
10,000 small random requests, 67% reads,exponentially sized with mean 4KB.
David Nagle December, 2000http://www.chips.ece.cmu.edu
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)
MEMS has smallpositioning variability
MEMS has smallpositioning variability
David Nagle December, 2000http://www.chips.ece.cmu.edu
PostMark - 5X Speedup
0
100
200
300
400
500
600
700
800
1999 Disk 2003 Disk MEMS
Storage Device Type
Ove
rall
Run
time
(s)
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
Baseline Configuration
File SystemFile System
DiskDisk Disk Disk
David Nagle December, 2000http://www.chips.ece.cmu.edu
Disk Cache Configuration
File SystemFile System
MEMSMEMSMEMSMEMS MEMSMEMS MEMSMEMS
David Nagle December, 2000http://www.chips.ece.cmu.edu
Disk Cache Configuration
File SystemFile System
Disk
MEMSCache
MEMSCache
Disk
MEMSCache
MEMSCache
Disk
MEMSCache
MEMSCache
Disk
MEMSCache
MEMSCache
David Nagle December, 2000http://www.chips.ece.cmu.edu
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)
David Nagle December, 2000http://www.chips.ece.cmu.edu
File System-managed Layout
• File system could allocate data directly
MEMSMEMS Disk
File systemFile system
• Metadata• Small files• Paging
• Large, streaming files
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
PostMark
0
500
1000
1500
2000
2500
3000
3500
Travelstar MEMS
Storage Device Type
Ene
rgy
(Jou
les)
3111
58
David Nagle December, 2000http://www.chips.ece.cmu.edu
PostMark
0
500
1000
1500
2000
2500
3000
3500
Travelstar MEMS
Storage Device Type
Ene
rgy
(Jou
les)
Performance IdlePerformance Idle
ActiveActive
ActiveActive
David Nagle December, 2000http://www.chips.ece.cmu.edu
Netscape
0
1000
2000
3000
4000
5000
6000
7000
Travelstar MEMS
Storage Device Type
Ene
rgy
(Jou
les)
6097
349
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
Future of MEMS-based Storage
• Perfect for portable devices• Size, capacity, power
David Nagle December, 2000http://www.chips.ece.cmu.edu
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
David Nagle December, 2000http://www.chips.ece.cmu.edu
MEMS-based Storage at CMU
lcs.web.cmu.edu/research/[email protected]