Flash Mem Summit 08 Tdinkelman Ssd
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Transcript of Flash Mem Summit 08 Tdinkelman Ssd
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SSDsA Shift in Data Storage
Todd Dinkelman
Micron Technology, Inc.
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Agenda
SSD Defined
Quick Comparison
Why MLC
Reliability/Endurance Summary
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What is Being Called an SSD?
USB interface embedded solution
Module-based
IDE interface card w/o enclosure
1.8-inch and 2.5-inch, 32GB and 64GB SSDfor notebook and performance computing
Module/card with custom form factor, density,
and interface
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The Complexity of HDDs
Base casting
SpindleSlider (and head)
Actuatorarm
Actuator axis
ActuatorSATA interfaceconnector Power connector
Flex circuit(attaches headsto logic board)Source: Panther Products
Platters
Cover mounting holes HDD Advantages
Density
Price/GB
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The Simplicity of SSDs
SATA interfaceconnector
ControllerNAND
Printed Circuit
SSD Advantages
Performance
Size
Weight
Ruggedness Temperature
Range
Power
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SSDs vs. HDDs
Temperature
Shock
Cost per bit
Weight
Size
Power
Endurance
Reliability
Performance
CapacityHDDsSSDs
Due to recent advances
in NAND lithography,SSD densities have
reached capacities for
mass market appeal
SSDs offer many
features that lead toimproved user
experiences
Early shortcomings
regarding reliability andendurance are being
overcome
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SSDs in Computing
10DRAM1,200
1,400L2 Cache2.5
1,800L1 Cache1
RelativeLatency RelativeCost/Bit
CPU
NAND Flash closes the latency gapCost/bit data as of November 2007
1HDD25,000,000
NAND 3SSD25,000
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MLC and SLC Differences
SLC Single-level cell
One bit per cell
MLC Multi-level cell
2 bits per cell today
3 and 4 bits per cell future
Endurance SLC is typically 10 times better than MLC
Performance
SLC provides ~2X the write performance of MLC
Price SLC-based products have better than 2X the
price/GB compared to MLC
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SSD Market Trends
Improvements in controller technology Moving from CompactFlash architectures to true
SSD controllers
Notebooks and PCs Migration to MLC
Light usage model
Cost, size, and performance are all important
Value Proposition Better than desktop performance in an ultra-light
notebook
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SSD Average Price/GB
2004 2006 2008 2010 2012 2014
$/GB
1.8" HDD
MLC SSD
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NAND Reliability and Endurance
Endurance/
Cycling
Data
Retention
Read
Disturb
Program
Disturb
Effect
Endurance
Reliability
ECC and Block
Management
Increased read
errors immediately
after programming
Cells not beingprogrammed
receive charge
via elevated
voltage stress
ECC and Block
Management
Increased read
errors with time
Charge loss over
time
Retire Block
Failed
program/erase
status
Cycles cause
charge trapped in
dielectric
ECC and Block
Management
Increased read
error at high
number of reads
Cells not beingread receive
charge via
elevated voltage
stress
ManagementObserved AsDescription
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NAND Error Rate
Bit Error Rate Failing bits corrected with appropriate levels of ECC
Correctable bit errors do not result in data loss
Raw Bit Error Rate (RBER): Bit error rate
prior to ECC
Uncorrectable Bit Error Rate (UBER): Bit
error rate after ECC
UBER is projected using the measured RBER
and specific level of ECC
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SSD Reliability and Endurance
SSD reliability has two parts
MTBF
Measure of time between failures due to manufacturing or
component defects
2 million hours is typical for Micron SSDs
Endurance
SSDs all wear out due to data writes
Indication of drive life based on a usage condition
Micron SSDs are specified to last 5 years under predefined
usage conditions
Usage conditions vary for consumer and performance products
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Endurance Factors
Wear-leveling efficiency
Write amplification
NAND cycles
SSD densities
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Wear-Leveling Example
MLC devices can typically support 10,000 cycles per
block
If you erased and reprogrammed one block every
second, you would exceed the 10,000 cycling limit in
just 3 hours!60 x 60 x 3 = 10,080
Rather than cycling the same block, wear-leveling
involves distributing the number of blocks that are
cycled
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Wear-Leveling Example (continued)
An 8GB MLC-based SSD contains 32,768 independent
blocks (each block is 256KB of data)
If we took the previous example and distributed the cycles
over all 32,768 blocks, each block would have been
programmed once after 9 hours If you provided perfect wear-leveling on an 8GB drive, you
could erase and program a block every second, every day
for over 10 years!
10,000 X 32,768 327,680,000= = 3,792 days = 10.38 years
60 X 60 X 24 86,400
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Typical PC File Transfers
0
200
400
600
800
1000
1200
1400
1600
1800
Less than
4KB
4KB to
16KB
16KB to
32KB
32KB to
64KB
64KB to
128KB
128KB to
256KB
Greater
than
256KB
Transfer Size
Avg . Disk By tes Per Read/Write
Reads
Writes
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SSD Endurance Calculation
Write amplification and wear-leveling
efficiency must be accounted for when
calculating SSD lifetime
Life in Years = NAND Cycles * SSD CapacityAmplification Factor * GB/Year
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SSD Capacity Effect on Endurance
Years for SSD to Wear Out
32 64 128 256 512
Drive Capacity (GB)
Tim
eto
Failure
SSD life will double with every doubling of capacity
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