Explaining SSDs: The Price/Performance Trade-off
Summary
TLDRThis video from explainingcomputers.com dives into the intricacies of solid-state drives (SSDs), highlighting the impact of various flash storage types on SSD life expectancy. It explains the role of SLC cache in sustaining write speed and the distinctions between SSDs with and without DRAM. The script covers different NAND technologies like SLC, MLC, TLC, QLC, and 3D NAND, and their implications on program/erase cycles. It also discusses wear leveling, terabytes written (TBW) ratings, and the importance of SSD capacity for both storage needs and data change frequency. The video provides insights into SSD performance factors, including interface types, IOPS ratings, and the use of SLC cache to enhance write speeds. It concludes with a look at DRAM-less SSDs and their performance trade-offs, emphasizing the importance of choosing the right SSD based on specific requirements and the necessity of regular backups.
Takeaways
- 💾 SSDs have become more affordable with manufacturers using techniques to offer higher capacities at lower costs.
- 🔍 Understanding different flash storage types and their implications on SSD life expectancy is crucial.
- 🌟 SLC cache plays a significant role in determining sustained write speed for SSDs.
- 🔢 SSDs come in various form factors and use NAND logic gate technologies like floating gate and charge trap flash.
- 🔄 SSDs use wear-leveling techniques to distribute program/erase cycles evenly across the drive to extend life.
- 🚫 Never keep an SSD more than 90% full to maximize its lifespan.
- 📊 SSD manufacturers often express minimum life expectancy through the terabytes written (TBW) metric.
- 🔝 SSD capacity is a measure of both storage size and how frequently data changes.
- 💾 SSDs with higher IOPs (input/output operations per second) are preferable for system drives.
- 🔄 SSDs equipped with SLC cache can write data at higher speeds initially before data is migrated to slower TLC or QLC cells.
- 💡 DRAM-less SSDs are cheaper and consume less energy, but may have lower performance and reduced lifespan compared to DRAM-equipped SSDs.
Q & A
Why is it important to understand different types of flash storage for SSDs?
-It's important to understand different types of flash storage because they have implications for SSD life expectancy, sustained write speed, and overall cost-effectiveness. Knowing these differences helps users make informed decisions based on their storage needs and usage patterns.
What are the two common technologies used in flash memory chips for SSDs?
-The two common technologies used in flash memory chips for SSDs are floating gate and charge trap flash. These technologies differ in how they store and manage electrons to represent data.
How does the number of bits stored per cell in SSDs affect their life expectancy?
-The more bits stored per cell, the fewer program/erase (PE) cycles the SSD can sustain before failing. This is because as cells wear out, it becomes harder to accurately distinguish between different states, leading to a higher likelihood of errors and eventual failure.
What is the difference between SLC, MLC, TLC, and QLC in terms of data storage and life expectancy?
-SLC (Single Level Cell) stores one bit of data per cell and can sustain up to about 100,000 PE cycles. MLC (Multi-Level Cell) stores two bits per cell, TLC (Triple Level Cell) stores three bits, and QLC (Quad Level Cell) stores four bits. As the number of bits per cell increases, the usable PE cycles decrease, with MLC having around 3,000 cycles, TLC between 500 and 2,000, and QLC between 300 and 1,000.
What is the significance of 3D NAND technology in SSD manufacturing?
-3D NAND technology allows for more flash memory cells to be stacked on top of each other, fitting more cells in the same space. This increases the storage capacity of SSDs without changing the number of bits stored per memory cell. It's an indication of the SSD's manufacturing process and contributes to higher capacity drives.
How does wear leveling affect the lifespan of an SSD?
-Wear leveling is a technique used by SSDs to maximize their life expectancy by evenly distributing program/erase cycles across the drive. This is done at the block level and is most effective on drives with a reasonable amount of free space. It's recommended not to have an SSD more than 90% full to ensure longer life.
What does the term 'terabytes written' (TBW) refer to and how is it used to express SSD life expectancy?
-Terabytes written (TBW) is a value used by manufacturers to express the minimum life expectancy of their SSDs. It indicates the total amount of data that can be written to the SSD before it reaches the end of its lifespan. The TBW value varies with drive capacity, with larger drives typically having a higher TBW rating.
Why is it not recommended to use an SSD as a system drive if it's almost always full?
-Using an SSD as a system drive when it's almost always full can reduce its lifespan. This is because wear leveling, which helps extend SSD life, is most effective when there is sufficient free space on the drive. A drive that's constantly full has less room for wear leveling to operate effectively.
How does the presence of an SLC cache in an SSD affect its write performance?
-An SLC cache in an SSD allows for faster initial data writes because these cells can be written to more quickly than TLC or QLC cells. The SSD's controller writes incoming data to the SLC cache first, then moves it to slower storage during idle periods. The size of the SLC cache can significantly impact the duration for which the SSD can maintain its maximum write speed.
What is the role of DRAM in SSDs and how do DRAM-less SSDs operate?
-DRAM (Dynamic Random Access Memory) in SSDs serves as a cache to speed up performance and store a map of data as it's moved during wear leveling. DRAM-less SSDs operate without DRAM chips, which makes them cheaper and reduces energy consumption. They use a portion of their NAND flash cells to store the data map, which can reduce the drive's lifespan. However, recent DRAM-less SSDs using Host Memory Buffer (HMB) can access the host computer's RAM via the PCI interface, maintaining performance and lifespan.
How do the different SSD technologies (SLC, MLC, TLC, QLC) and their respective life expectancies impact the choice of an SSD for a specific use case?
-The choice of an SSD for a specific use case depends on the required life expectancy and sustained write requirements. For example, an SLC SSD with a high number of PE cycles is suitable for write-intensive applications, while a QLC SSD with fewer cycles may be more appropriate for read-heavy tasks. The user's specific needs, such as the frequency of data changes and the amount of data to be stored, should guide the selection of the SSD technology.
What precautions should be taken when using SSDs for data storage?
-SSDs, while reliable and fast, are not permanent data stores. It's important to take precautions such as regular data backups and using encryption to ensure data security and integrity. This is especially crucial given that SSDs have a limited number of program/erase cycles, after which they may fail.
Outlines
💾 SSD Technology and Life Expectancy
This paragraph introduces the topic of solid-state drives (SSDs), focusing on their cost-effectiveness and the various techniques used to increase storage capacity. It explains the differences between single-level cell (SLC), multi-level cell (MLC), triple-level cell (TLC), and quad-level cell (QLC) flash memory, which determine the number of bits stored per cell and the number of program/erase cycles each can sustain. The paragraph also touches on the concept of 3D NAND and V-NAND, which increase storage density without changing the number of bits per cell. The importance of understanding these technologies is highlighted in relation to SSD life expectancy.
🔄 SSD Performance and Wear Leveling
The second paragraph delves into SSD performance, wear leveling, and the concept of terabytes written (TBW) as a measure of SSD life expectancy. It explains how wear leveling distributes program/erase cycles evenly across the drive to extend its lifespan, and the importance of maintaining free space on the SSD to facilitate this process. The paragraph also discusses how SSD capacity relates to the frequency of data changes, using examples to illustrate how different SSD capacities can meet different needs based on TBW ratings. It provides specific examples of Samsung SSDs with different types of flash memory and their respective TBW ratings, emphasizing the trade-offs between capacity, performance, and endurance.
🚀 SSD Speed, SLC Cache, and DRAM-less SSDs
This paragraph discusses the factors affecting SSD read and write speeds, including the interface type (PCIe vs. SATA/SAS) and the IOPS rating. It explains the role of SLC cache in SSDs, which temporarily stores data at a faster rate before transferring it to slower TLC or QLC cells. The paragraph demonstrates the performance impact of SLC cache size through a data transfer example, highlighting how sustained write speeds can be affected once the cache is full. It also addresses DRAM-less SSDs, which omit DRAM chips to reduce cost and energy consumption, and how the introduction of Host Memory Buffer (HMB) in the NVMe standard has improved the performance and life expectancy of these drives. The paragraph concludes by emphasizing the importance of considering specific requirements for life expectancy and sustained write speed when choosing an SSD, and the need for regular backups due to the non-permanent nature of SSD storage.
Mindmap
Keywords
💡Solid-State Drives (SSDs)
💡Flash Storage
💡SLC Cache
💡Program/Erase (P/E) Cycles
💡Wear Leveling
💡Terabytes Written (TBW)
💡3D NAND
💡IOPS (Input/Output Operations Per Second)
💡DRAM-less SSDs
💡Host Memory Buffer (HMB)
Highlights
SSD storage costs have never been lower, and manufacturers are using techniques to offer higher capacities at minimal costs.
Understanding different flash storage types and their implications for SSD life expectancy is crucial.
SLC cache plays a role in determining sustained write speed in SSDs.
SSDs without DRAM have differences compared to those with DRAM, impacting performance and cost.
SSDs come in various form factors and physical connectors but store data on flash memory chips in grids of cells.
Two common technologies used in NAND flash are floating gate and charge trap flash.
NAND flash cells can be individually written but erased in blocks, affecting SSD lifespan.
SSDs have evolved from SLC, which stores one bit per cell, to MLC, TLC, QLC, and soon PLC, increasing storage capacity but reducing lifespan.
3D NAND and V-NAND are manufacturing processes that increase cell density without changing bits per cell.
Wear leveling is a technique used in SSDs to maximize life expectancy by distributing program/erase cycles.
SSD life expectancy is often expressed via a TBW (Terabytes Written) value, which varies with drive capacity.
SSD capacity is a measure of both data storage needs and how frequently data changes.
SSD read/write speed depends on factors including the interface and IOPS rating.
SSDs with more bits per cell, like TLC and QLC, are slower to write data and often include an SLC cache to improve speed.
The size of an SSD's SLC cache affects how long it can write data at maximum speed.
DRAM-less SSDs have been developed to reduce cost and energy consumption, using HMB to access host computer RAM.
Modern SSDs from major manufacturers offer excellent performance and reliability, with choices depending on specific needs.
SSDs are not permanent data stores, and it's important to take precautions with backups and encryption.
Transcripts
[Music]
welcome to another video from explaining
computers.com
this time we're going to return to one
of my favorite subjects which is
solidstate drives or
ssds today the cost of SSD storage has
never been so low however manufacturers
are using a number of techniques to
offer higher and higher capacity drives
for a minimum cost it's therefore
important to understand the different
types of flash storage and their
implications for SSD life expectancy the
role of SLC cache in determining
sustained right speed and the difference
between ssds with and without D
Ram
as I've detailed in another video today
ssds come in a variety of form factors
and may feature many different physical
connectors and electrical
interfaces however all ssds store data
on flash memory chips in grids of cells
that are grouped into
blocks specifically in most ssds the
memory cells are Nan's logic gates two
Tech Technologies are commonly used
named floating gate and charge trap
Flash in either to write or program data
a voltage is applied to move electrons
into a floating gate or charge trap the
presence of these electrons changes the
resistance between the memory cells
source and drain and this can be
measured by passing a current between
them whilst n flash cells can be
individually written they could only be
erased in blocks to do this a voltage or
field is applied to remove the electrons
from the floating gate or charge trap
however repeated program erase
operations weaken the material cells are
made from which result in electrons
either escaping a floating gate or being
retained in a CH trap after a certain
number of program erase or PE Cycles it
therefore becomes impossible for the
cell to reliably function and the
Practical implication is that all ssds
can only sustain a limited number of
data right operations before they
fail the number of program array cycles
that a memory cell can sustain in part
depends on how much data it has to hold
initially all ssds stored just one bit
of data per flash memory cell which we
now refer to as single level cell or
SLC however to scale up Capac capacities
for a reasonable cost multi-level cell
or mlc was developed this stores two
bits per memory cell and does so by
distinguishing two additional States
between fully programmed and fully
erased however as the cell wears out and
electrons stray it's more difficult to
accurately distinguish four different
states compared to two and so mlc ssds
have a smaller number of usable program
aray Cy Les than SLC
devices in turn we next saw the arrival
of triple level cell or TLC ssds which
store three bits of data per cell and
then quad level cell or qlc drives that
store guess what four bits of data for
cell pent level cell or PLC ssds are
also now close to
Market given that TLC qlc and PLC have
to act accurately distinguish an
increasing number of partially
programmed States it's inevitable that
they offer fewer and fewer programmer
race Cycles the number of Cycles is
different for Consumer and Enterprise
hardware and also varies between models
and
manufacturers but as a guide SLC drives
can sustain up to about 100,000
programmer raise Cycles consumer mlc up
to about 3,000 TLC somewhere between 500
and 2,000 and qlc between about 300 and
1,000 as another means of increasing
capacity ssds are now often manufactured
with many layers of flash memory cells
stacked on top of each other this fits
more cells in the same space and is
known by several different names
including 3D nand and vand however it
doesn't change the number of bits stored
per memory cell and so from a user
perspective is simply an indication of
an ssd's manufacturing
process in order to maximize their life
expectancy ssds use a technique called
wear leveling that moves data around the
drive in order to even out program erase
Cycles this occurs at the Block Level
and can happen most effectively on
drives with a reasonable amount of free
space so if possible it's wise to never
have an SSD more than 90% full in order
to make it last
longer today manufacturers usually
Express the minimum life expectancy of
their ssds via terabytes written or tbw
value but inevitably varies with drive
capacity for example if we have 1 2 and
4 terabyte ssds based on the same TLC
flash with a minimum of 500 program
erase Cycles then the one 1 terabyte
drive will be rated 500 terabyt written
the 2 tbte 1,000 terabyt written and the
4 terabyte 2,000 terab written this
highlights how today SSD capacity has
become a measure not just of how much
data we want to store but how frequently
we want to change
it for example if you're purchasing an
SSD to uses a system drive that will
contain lots of program and data files
that rarely change then the 1 terb SSD
may be an excellent choice as 500 terab
written equates to 100 GB written every
day for 5,000 days which is 13.7 years
however if you need to record and raise
2 hours of raw 4K video every day then
the 1 tbte drive would hit life
expectancy in 18 months whilst the 4
terb model could last 6
years
to provide some practical examples here
I've got three 1 tbte Samsung
ssds the product names indicate that
this 860 pro drive is mlc or what
Samsung term 2 bit mlc whilst this 870
Evo is TLC or what Samsung would
helpfully call 3-bit
mlc and on the end this 860 CUO is qlc
or what Samsung choose to label 4bit
mlc and why Samsung cannot stick to
standard terms is one of the many great
mysteries of
computing anyway the 1 tbte mlc Pro is
rated for 12200 terabyt written the TLC
Evo for 600 and the qlc CUO for
360 and sadly whilst the pro drive will
last longer as Drive capacities increase
this is no longer deemed relevant for
client devices and so like most
manufacturers Samsung sadly no longer
make 2bit mlc consumer
ssds the speed at which an SSD can read
and write data depends on many factors
as we can see one of these is its
interface with drives using the most
recent PCI mvme connections having the
opportunity to transfer data
considerably faster than ssds which
utilize SATA or SAS this said SSD
performance depends on far more than its
interface for start cheaper ssds
generally have a lower iops or input
output operations per second rating this
measures how many different read and
write operations can occur every second
and can vary from a few thousand to over
a million
so if you're comparing two ssds to use
as a system Drive always go for the one
with a higher IOP
specification returning to SSD
Technologies the more bits are stored in
each memory cell the slower data can be
written and because TLC and qlc Flash
write data far more slowly the most SSD
interfaces can deliver modern drives are
equipped with an SLC cash
this means that the SSD has some flash
memory cells configured to store just
one bit of data which can be written to
far more quickly so the ssd's controller
initially writes incoming data to its
SLC cells before migrating it to slower
TLC or qlc in idle
periods to illustrate this let's copy 36
GB of data to a 500 GB Samsung 970 Evo
plus m.2 mvme
SSD as we can see things initially speed
along but after 22 GB of data transfer
the drive's SLC cache is full and right
performance collapses from its previous
level of about 2.7 GB a
second things then take a while to
settle with the right speed finally
stabilizing at about 800 megab a second
for the remainder of the
copy clearly the more SLC cache and SSD
possesses the longer it will be able to
write data at its maximum
speed and the larger the drive the more
SLC cache it will possess for example
whilst the 500 GB Evo 970 plus we just
tested has 22 GB of SLC cache the 1
terabyte model has 42 GB
it's also worth noting that some ssds
now have a dynamic SLC cache that can
expand by reconfiguring empty TLC or qlc
cells as
SLC thankfully Samsung publishes the
size of the SLC cache on its ssds
something it labels as turbo right but
sadly some other manufacturers do not
reveal SLC cash size
information however if the sustained
high-speed right of many tens of
gigabytes of data matters for your
workflow I would strongly advise
obtaining test results to find out how
large a drive's SLC cache may be before
you
purchase in addition to using TLC and
qlc in recent years manufacturers have
started to make dram less
ssds dram or Dynamic random access
memory only retains data when powered
and has traditionally been included on
ssds as a cache to speed up performance
as well as to store a map of data as
it's moved around during we
leveling but daml ssds have no dram
chips which makes them cheaper and
reduces energy
consumption however dram L ssds still
need to perform we leveling and so first
generation drumless ssds store a map of
Drive contents on some of their nand
flash cells so reducing the life of the
drive until recently if you purchased a
dless SSD you therefore got a cheaper
drive but also one with lower
performance and a reduced life
expectancy however in the past few years
dramas ssds from Samsung Western Digital
and others have started to make use of a
new mvme standard called host memory
buffer or a
hmb this allows the SSD to access some
of the host computers Ram via the PCI
interface which means that hmb dless
ssds do not have a reduced life
expectancy they are however still slower
than dram ssds although this only tends
to matter for intensive applications
like video editing or playing the latest
games but if you're not using your
computer for these things a DE rless SSD
do offer a good price performance
tradeoff today ssds from all major
manufacturers provide excellent
performance and reliability compared to
drives from just a few years ago and so
for General use it often doesn't make
that much difference which kind of SSD
you
choose however if you you have specific
life expectancy or sustained right
requirements it is important to pay
attention to the characteristics of a
particular drive and of course you've
always got to be aware that no SSD is
ever a permanent data store and
therefore to take precautions as covered
in my video cyber security backups and
encryption but now that's it for another
video if you've enjoyed what you've seen
here please press that like button if
you haven't subscribed Please Subscribe
and I hope to talk to you again very
[Music]
soon
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