Explaining SSDs: The Price/Performance Trade-off

Summary

This 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

00:00

💾 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.

05:01

🔄 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.

10:04

🚀 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.

Keywords

💡Solid-State Drives (SSDs)

Solid-State Drives, or SSDs, are a type of non-volatile storage device that store data on flash memory chips. They are known for their fast data access speeds and reliability compared to traditional hard drives. In the video, SSDs are the main focus, discussing their cost-effectiveness, capacity, and different types of flash storage that affect their life expectancy and performance.

💡Flash Storage

Flash storage is a type of non-volatile storage technology that retains data even when power is not present. It is the core component of SSDs. The video explains that different types of flash storage, such as SLC, MLC, TLC, and QLC, have varying capacities and endurance levels, which are crucial for understanding the lifespan and performance of SSDs.

💡SLC Cache

SLC Cache refers to a portion of the SSD's flash memory that is configured to store data at a faster speed, similar to how Single-Level Cell (SLC) flash memory operates. The video demonstrates the importance of SLC cache in determining the sustained write speed of an SSD, showing how performance can degrade once the cache is full.

💡Program/Erase (P/E) Cycles

Program/Erase cycles are the number of times a flash memory cell can be written to and erased before it becomes unreliable. The video emphasizes that this metric is vital for SSD life expectancy, with different types of flash memory (SLC, MLC, TLC, QLC) supporting different numbers of P/E cycles.

💡Wear Leveling

Wear leveling is a technique used in SSDs to distribute write and erase cycles evenly across the memory cells to prolong the drive's lifespan. The video mentions that wear leveling is more effective when there is a reasonable amount of free space on the SSD, advising against filling an SSD to more than 90% capacity.

💡Terabytes Written (TBW)

Terabytes Written is a measure used by manufacturers to express the minimum life expectancy of an SSD in terms of the total amount of data that can be written to it. The video uses TBW as an example to illustrate how SSD capacity and life expectancy are related, with larger drives having higher TBW ratings.

💡3D NAND

3D NAND is a manufacturing process where flash memory cells are stacked in layers to increase storage density in the same physical space. The video explains that while 3D NAND increases capacity, it does not change the number of bits stored per memory cell and is an indicator of the SSD's manufacturing process.

💡IOPS (Input/Output Operations Per Second)

IOPS stands for Input/Output Operations Per Second and is a performance metric that measures how many separate read and write operations an SSD can perform each second. The video notes that cheaper SSDs often have lower IOPS ratings, which can affect their overall performance.

💡DRAM-less SSDs

DRAM-less SSDs are solid-state drives that do not include DRAM chips, which are traditionally used for caching and mapping data during wear leveling. The video discusses how these drives can be cheaper and consume less power but may have lower performance and reduced lifespans, although new standards like HMB have mitigated some of these issues.

💡Host Memory Buffer (HMB)

Host Memory Buffer, or HMB, is a feature of the NVMe standard that allows DRAM-less SSDs to use some of the host computer's RAM for caching and mapping data. The video explains that HMB enables DRAM-less SSDs to have similar performance and lifespans as those with DRAM, without the need for onboard DRAM chips.

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

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and I hope to talk to you again very

[Music]

soon