A Shift in Data Storage Todd Dinkelman Micron Technology, Inc.
A Shift in Data Storage Todd Dinkelman Micron Technology, Inc.
A Shift in Data Storage Todd Dinkelman Micron Technology, Inc.
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
SSDs<br />
A <strong>Shift</strong> <strong>in</strong> <strong>Data</strong> <strong>Storage</strong><br />
<strong>Todd</strong> D<strong>in</strong>kelman<br />
<strong>Micron</strong> <strong>Technology</strong>, <strong>Inc</strong>.<br />
Santa Clara, CA USA<br />
August 2008 1
Agenda<br />
� SSD Def<strong>in</strong>ed<br />
� Quick Comparison<br />
� Why MLC<br />
� Reliability/Endurance<br />
� Summary<br />
Santa Clara, CA USA<br />
August 2008 2
What is Be<strong>in</strong>g Called an SSD?<br />
� USB <strong>in</strong>terface embedded solution<br />
� Module-based<br />
� IDE <strong>in</strong>terface card w/o enclosure<br />
� 1.8-<strong>in</strong>ch and 2.5-<strong>in</strong>ch, 32GB and 64GB SSD<br />
for notebook and performance comput<strong>in</strong>g<br />
� Module/card with custom form factor, density,<br />
and <strong>in</strong>terface<br />
Santa Clara, CA USA<br />
August 2008 3
Sp<strong>in</strong>dle<br />
Slider (and head)<br />
Actuator<br />
arm<br />
Actuator<br />
SATA <strong>in</strong>terface<br />
connector<br />
Source: Panther Products<br />
Base cast<strong>in</strong>g<br />
The Complexity of HDDs<br />
Actuator axis<br />
Cover mount<strong>in</strong>g holes<br />
Power connector<br />
Platters<br />
Flex circuit<br />
(attaches heads<br />
to logic board)<br />
� HDD Advantages<br />
• Density<br />
• Price/GB<br />
Santa Clara, CA USA<br />
August 2008 4
SATA <strong>in</strong>terface<br />
connector<br />
The Simplicity of SSDs<br />
Controller<br />
Pr<strong>in</strong>ted Circuit<br />
NAND<br />
� SSD Advantages<br />
• Performance<br />
• Size<br />
• Weight<br />
• Ruggedness<br />
• Temperature<br />
Range<br />
• Power<br />
Santa Clara, CA USA<br />
August 2008 5
Capacity<br />
Performance<br />
Reliability<br />
Endurance<br />
Power<br />
Size<br />
Weight<br />
Shock<br />
Temperature<br />
Cost per bit<br />
SSDs vs. HDDs<br />
SSDs<br />
�<br />
�<br />
�<br />
�<br />
�<br />
�<br />
�<br />
�<br />
HDDs<br />
Santa Clara, CA USA<br />
August 2008 6<br />
�<br />
�<br />
�<br />
� Due to recent advances<br />
<strong>in</strong> NAND lithography,<br />
SSD densities have<br />
reached capacities for<br />
mass market appeal<br />
� SSDs offer many<br />
features that lead to<br />
improved user<br />
experiences<br />
� Early shortcom<strong>in</strong>gs<br />
regard<strong>in</strong>g reliability and<br />
endurance are be<strong>in</strong>g<br />
overcome
SSDs <strong>in</strong> Comput<strong>in</strong>g<br />
Relative<br />
Latency<br />
1,200<br />
L2 Cache<br />
DRAM<br />
1,400<br />
Santa Clara, CA USA<br />
Cost/bit data as of November 2007<br />
August 2008 7<br />
1<br />
2.5<br />
CPU<br />
L1 Cache<br />
Relative<br />
Cost/Bit<br />
1,800<br />
NAND 25,000<br />
SSD 3<br />
25,000,000<br />
HDD<br />
10<br />
NAND Flash closes the latency gap<br />
1
NAND <strong>in</strong> Computer Architecture<br />
DRAM<br />
DRAM<br />
USB<br />
Flash Drive<br />
DDR3<br />
USB<br />
CPU<br />
Memory<br />
& Bus<br />
Control<br />
L<strong>in</strong>k<br />
Peripheral<br />
& Bus<br />
Control<br />
SATA<br />
Hybrid<br />
HDD SSD<br />
PCIe Graphics<br />
PCIe<br />
NVMHCI<br />
Flash<br />
Santa Clara, CA USA<br />
August 2008 8
MLC and SLC Differences<br />
� SLC<br />
• S<strong>in</strong>gle-level cell<br />
– One bit per cell<br />
� MLC<br />
• Multi-level cell<br />
– 2 bits per cell – today<br />
– 3 and 4 bits per cell – future<br />
� Endurance<br />
• SLC is typically 10 times better than MLC<br />
� Performance<br />
� Price<br />
• SLC provides ~2X the write performance of MLC<br />
• SLC-based products have better than 2X the<br />
price/GB compared to MLC<br />
Santa Clara, CA USA<br />
August 2008 9
SSD Market Trends<br />
� Improvements <strong>in</strong> controller technology<br />
• Mov<strong>in</strong>g from CompactFlash architectures to true<br />
SSD controllers<br />
� Notebooks and PCs<br />
• Migration to MLC<br />
– Light usage model<br />
– Cost, size, and performance are all important<br />
• Value Proposition<br />
– Better than desktop performance <strong>in</strong> an ultra-light<br />
notebook<br />
Santa Clara, CA USA<br />
August 2008 10
$/GB<br />
SSD Average Price/GB<br />
1.8" HDD<br />
MLC SSD<br />
2004 2006 2008 2010 2012 2014<br />
Santa Clara, CA USA<br />
August 2008 11
Reliability<br />
Endurance<br />
NAND Reliability and Endurance<br />
Effect<br />
Program<br />
Disturb<br />
Read<br />
Disturb<br />
<strong>Data</strong><br />
Retention<br />
Endurance/<br />
Cycl<strong>in</strong>g<br />
Description<br />
Cells not be<strong>in</strong>g<br />
programmed<br />
receive charge<br />
via elevated<br />
voltage stress<br />
Cells not be<strong>in</strong>g<br />
read receive<br />
charge via<br />
elevated voltage<br />
stress<br />
Charge loss over<br />
time<br />
Cycles cause<br />
charge trapped <strong>in</strong><br />
dielectric<br />
Observed As<br />
<strong>Inc</strong>reased read<br />
errors immediately<br />
after programm<strong>in</strong>g<br />
<strong>Inc</strong>reased read<br />
error at high<br />
number of reads<br />
<strong>Inc</strong>reased read<br />
errors with time<br />
Failed<br />
program/erase<br />
status<br />
Management<br />
ECC and Block<br />
Management<br />
ECC and Block<br />
Management<br />
ECC and Block<br />
Management<br />
Retire Block<br />
Santa Clara, CA USA<br />
August 2008 12
NAND Error Rate<br />
� Bit Error Rate<br />
– Fail<strong>in</strong>g bits corrected with appropriate levels of ECC<br />
– Correctable bit errors do not result <strong>in</strong> data loss<br />
� Raw Bit Error Rate (RBER): Bit error rate<br />
prior to ECC<br />
� Uncorrectable Bit Error Rate (UBER): Bit<br />
error rate after ECC<br />
� UBER is projected us<strong>in</strong>g the measured RBER<br />
and specific level of ECC<br />
Santa Clara, CA USA<br />
August 2008 13
SSD Reliability and Endurance<br />
� SSD reliability has two parts<br />
• MTBF<br />
– Measure of time between failures due to manufactur<strong>in</strong>g or<br />
component defects<br />
– 2 million hours is typical for <strong>Micron</strong> SSDs<br />
• Endurance<br />
– SSDs all wear out due to data writes<br />
– Indication of drive life based on a usage condition<br />
– <strong>Micron</strong> SSDs are specified to last 5 years under predef<strong>in</strong>ed<br />
usage conditions<br />
– Usage conditions vary for consumer and performance products<br />
Santa Clara, CA USA<br />
August 2008 14
Endurance Factors<br />
� Wear-level<strong>in</strong>g efficiency<br />
� Write amplification<br />
� NAND cycles<br />
� SSD densities<br />
Santa Clara, CA USA<br />
August 2008 15
Wear-Level<strong>in</strong>g<br />
� Dynamic wear-level<strong>in</strong>g uses the available<br />
free space and the <strong>in</strong>com<strong>in</strong>g data to equally<br />
wear each of the physical blocks<br />
• Static data is not <strong>in</strong>cluded <strong>in</strong> the available pool of<br />
wear-level<strong>in</strong>g blocks, leav<strong>in</strong>g a portion of the drive<br />
with no wear<br />
� Static wear-level<strong>in</strong>g considers all physical<br />
blocks <strong>in</strong> the SSD, regardless of content, and<br />
ma<strong>in</strong>ta<strong>in</strong>s an even level of wear across the<br />
entire drive<br />
Santa Clara, CA USA<br />
August 2008 16
Wear-Level<strong>in</strong>g Example<br />
� MLC devices can typically support 10,000 cycles per<br />
block<br />
� If you erased and reprogrammed one block every<br />
second, you would exceed the 10,000 cycl<strong>in</strong>g limit <strong>in</strong><br />
just 3 hours!<br />
60 x 60 x 3 = 10,080<br />
� Rather than cycl<strong>in</strong>g the same block, wear-level<strong>in</strong>g<br />
<strong>in</strong>volves distribut<strong>in</strong>g the number of blocks that are<br />
cycled<br />
Santa Clara, CA USA<br />
August 2008 17
Wear-Level<strong>in</strong>g Example (cont<strong>in</strong>ued)<br />
� An 8GB MLC-based SSD conta<strong>in</strong>s 32,768 <strong>in</strong>dependent<br />
blocks (each block is 256KB of data)<br />
� If we took the previous example and distributed the cycles<br />
over all 32,768 blocks, each block would have been<br />
programmed once after 9 hours<br />
� If you provided perfect wear-level<strong>in</strong>g on an 8GB drive, you<br />
could erase and program a block every second, every day<br />
for over 10 years!<br />
10,000 X 32,768 327,680,000<br />
= = 3,792 days = 10.38 years<br />
60 X 60 X 24 86,400<br />
Santa Clara, CA USA<br />
August 2008 18
Write Amplification<br />
� Additional write overhead due to garbage collection<br />
and wear-level<strong>in</strong>g<br />
• Write Amplification = Flash Writes / Host Writes<br />
� Influence on host data patterns<br />
• Large number of small random transfers <strong>in</strong>creases write<br />
amplification<br />
� Influenced by number of spare blocks and static data<br />
• Keep<strong>in</strong>g a percentage of the drive as spares will bound the<br />
write amplification<br />
Santa Clara, CA USA<br />
August 2008 19
1800<br />
1600<br />
1400<br />
1200<br />
1000<br />
800<br />
600<br />
400<br />
200<br />
0<br />
Typical PC File Transfers<br />
Less than<br />
4KB<br />
4KB to<br />
16KB<br />
Avg. Disk Bytes Per Read/Write<br />
16KB to<br />
32KB<br />
32KB to<br />
64KB<br />
Transfer Size<br />
64KB to<br />
128KB<br />
128KB to<br />
256KB<br />
Greater<br />
than<br />
256KB<br />
Reads<br />
Writes<br />
Santa Clara, CA USA<br />
August 2008 20
SSD Endurance Calculation<br />
� Write amplification and wear-level<strong>in</strong>g<br />
efficiency must be accounted for when<br />
calculat<strong>in</strong>g SSD lifetime<br />
Life <strong>in</strong> Years =<br />
NAND Cycles * SSD Capacity<br />
Amplification Factor * GB/Year<br />
Santa Clara, CA USA<br />
August 2008 21
SSD Lifetime<br />
� Given a capacity po<strong>in</strong>t, NAND endurance, and writes-per-day, the<br />
upper limit on SSD lifetime is def<strong>in</strong>ed<br />
• Example: A 64GB SSD, 10K PROGRAM/ERASE cycles and write duty of<br />
350 GB/day will wear out <strong>in</strong> 5 years<br />
� Uneven wear with<strong>in</strong> a NAND Flash device may cause ‘hot spots’<br />
• Wear-level<strong>in</strong>g of NAND is necessary<br />
� Improper NAND data management may cause lifetime to be<br />
significantly less than the limit<br />
• A Flash ERASE operation must occur before a page can be rewritten<br />
• To improve overall throughput, erase granularity is much larger than write<br />
granularity<br />
• LBA traffic pattern can cause lots of extra data movement<br />
Santa Clara, CA USA<br />
August 2008 22
Times per Day (Count)<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
SSD Endurance<br />
Average Number Of Times Per Day The Drive Space Gets Written<br />
0 12 24 36 48 60 72 84 96<br />
Required Lifetime (Months)<br />
33% WRITEs<br />
2K random IOPs<br />
64GB drive<br />
(55GB user-accessible<br />
20% reserved spares<br />
Santa Clara, CA USA<br />
August 2008 23
Time to Failure<br />
SSD Capacity Effect on Endurance<br />
Years for SSD to Wear Out<br />
32 64 128 256 512<br />
Drive Capacity (GB)<br />
� SSD life will double with every doubl<strong>in</strong>g of capacity<br />
Santa Clara, CA USA<br />
August 2008 24
Summary<br />
� SSDs br<strong>in</strong>g many advantages to storage<br />
• Performance<br />
• Power<br />
• Reliability<br />
• Environmental ruggedness<br />
� Different products for different markets<br />
• MLC-based SSDs for PCs<br />
� Reliability has two aspects<br />
• Endurance and MTBF<br />
Santa Clara, CA USA<br />
August 2008 25
Thank You<br />
Santa Clara, CA USA<br />
August 2008 26
Change language