Would You Rather QLC w/DRAM or TLC without?

[Generalkidd]

There was a huge sale on Newegg recently where the 1 TB Samsung QVO 870 was going for like $79 which put it very close to ultra cheap DRAM-less SSDs like the TeamGroup CX1 1 TB SSD. I did end up getting the Samsung SSD because ironically my current TeamGroup SSD (GX2) seems to have failed on me and even before it failed the performance was often times pretty bad on this laptop. But I'm wondering if I made the right choice going with QLC. I'm aware of the significant downsides of QLC memory but was hoping the DRAM and SLC cache would make up for it compared to a DRAM-less TLC SSD. But what are your thoughts about this? Would you rather go for a QLC SSD that has DRAM or a cheaper TLC SSD without DRAM? 

[Bombastinator]

3 minutes ago, Generalkidd said:

There was a huge sale on Newegg recently where the 1 TB Samsung QVO 870 was going for like $79 which put it very close to ultra cheap DRAM-less SSDs like the TeamGroup CX1 1 TB SSD. I did end up getting the Samsung SSD because ironically my current TeamGroup SSD (GX2) seems to have failed on me and even before it failed the performance was often times pretty bad on this laptop. But I'm wondering if I made the right choice going with QLC. I'm aware of the significant downsides of QLC memory but was hoping the DRAM and SLC cache would make up for it compared to a DRAM-less TLC SSD. But what are your thoughts about this? Would you rather go for a QLC SSD that has DRAM or a cheaper TLC SSD without DRAM? 

Is dram the right word here?  Dram is what happened befor SDRAM which is what happened before ddr1.

[SquintyG33Rs]

don't get anything that actually has no DRAM. but the on controller ram options are often totally fine (they do have it, it's just not an external chip)

 

TLC vs QLC don't seem to make much of a difference in real world performance. I'd just get whatever is the cheaper option tbh.

[Generalkidd]

3 minutes ago, Bombastinator said:

Is dram the right word here?  Dram is what happened befor SDRAM which is what happened before ddr1.

DRAM is just the term for "Dynamic Random Access Memory" which applies to all forms of RAM. DDR5, DDR4, etc are all DRAM. It does not specify a specific generation of RAM. Also, SDRAM isn't a generation of RAM that predated DDR1, it's a type of DRAM that includes all modern forms of RAM. Even the latest DDR5 is still SDRAM. 

[Generalkidd]

3 minutes ago, SquintyG33Rs said:

don't get anything that actually has no DRAM. but the on controller ram options are often totally fine (they do have it, it's just not an external chip)

 

TLC vs QLC don't seem to make much of a difference in real world performance. I'd just get whatever is the cheaper option tbh.

In this case, the TeamGroup TLC SSD was only like $5-7 cheaper so I figured it was better to spend a few extra dollars and get the Samsung SSD. I just wasn't sure if QLC is so bad that having a DRAM cache couldn't make up for it compared to a DRAM-less SSD. 

[Bombastinator]

The thing about SSDs is they’re so unbelievably fast even something twice as fast almost doesn’t matter.  Fractions of a second differences. Cache dramatically increases efficiency of the device though which makes it last longer.  Fewer writes.  Better wear leveling. I’ve heard some cacheless SSDs can use ram as cache though, so cacheless stuff can get the advantages of cache SSDs at the cost of a bit of total ram. Some do some don’t though.  Or something.

[Bombastinator]

5 minutes ago, Generalkidd said:

DRAM is just the term for "Dynamic Random Access Memory" which applies to all forms of RAM. DDR5, DDR4, etc are all DRAM. It does not specify a specific generation of RAM. Also, SDRAM isn't a generation of RAM that predated DDR1, it's a type of DRAM that includes all modern forms of RAM. Even the latest DDR5 is still SDRAM. 

Not all.  Just the cheaper ram.  Sram is a pile faster, but it’s more expensive and uses more real estate.  Stan has other advantages too, like it doesn’t need to be constantly refreshed. SRAM is what stuff like lv.1 cache in the cpu uses.

Edited February 24, 2022 by Bombastinator

[SquintyG33Rs]

Just now, Generalkidd said:

In this case, the TeamGroup TLC SSD was only like $5-7 cheaper so I figured it was better to spend a few extra dollars and get the Samsung SSD. I just wasn't sure if QLC is so bad that having a DRAM cache couldn't make up for it compared to a DRAM-less SSD. 

yeah. but i'm not sure if it's truly one of the dram-less SSD. I can't find the information on it quickly (probably because it's an older product)

If it is, it's not worth saving 5$...

[SquintyG33Rs]

3 minutes ago, Bombastinator said:

The thing about SSDs is they’re so unbelievably fast even something twice as fast almost doesn’t matter.  Fractions of a second differences. Cache dramatically increases efficiency of the device though which makes it last longer.  Fewer writes.  Better wear leveling. I’ve heard some cacheless SSDs can use ram as cache though, so cacheless stuff can get the advantages of cache SSDs at the cost of a bit of total ram. Some do some don’t though.  Or something.

sorry to burst your bubble but he's asking about 2 sata SSD. we're not talking about direct access nvme with SAM or anything.

[Bombastinator]

3 minutes ago, SquintyG33Rs said:

sorry to burst your bubble but he's asking about 2 sata SSD. we're not talking about direct access nvme with SAM or anything.

In that case then there’s no difference at all speed wise because the sata3 bottleneck is so narrow even the cheap stuff can max it out.  It might be that anything on a sata port would be too slow to use system ram for cache.  SSDs are so much faster than 6Gb/sec. It’s not even funny.  Even the slow ones. If your SSD is on sata, the speed is effectively capped, so you might as well get the stuff with the best longevity.

[Generalkidd]

Just now, Bombastinator said:

In that case then there’s no difference at all speed wise because the sata3 bottleneck is so narrow even the cheap stuff can max it out.  It might be that anything on a sata port would be too slow to use system ram for cache.

An SSD with DRAM isn't using the system RAM for cache, it means the SSD has its own onboard DRAM. Plus there's more to an SSD than just the transfer speeds of the SATA connector. 

[SquintyG33Rs]

3 minutes ago, Bombastinator said:

In that case then there’s no difference at all speed wise because the sata3 bottleneck is so narrow even the cheap stuff can max it out.  It might be that anything on a sata port would be too slow to use system ram for cache.

no under sequential writes the DRAM will make a difference and the performance will crumble on the cacheless drive much faster.

actually a cache-less drive becomes unbearably slow once it's filled up because it was using free space as cache and it can't do that anymore. for eveyrday windows if you never use more than 80% capacity it probably won't show a difference but once full the cache-less drive is slower than HDD while the Samsung would still do pretty good.

[Bombastinator]

2 minutes ago, Generalkidd said:

An SSD with DRAM isn't using the system RAM for cache, it means the SSD has its own onboard DRAM. Plus there's more to an SSD than just the transfer speeds of the SATA connector. 

Yes.  That is what I was saying.  There’s also lower latency, but again, SSDs are still way way faster than HDDs that way.  Getting into those fractional differences again. 

[Generalkidd]

10 minutes ago, SquintyG33Rs said:

yeah. but i'm not sure if it's truly one of the dram-less SSD. I can't find the information on it quickly (probably because it's an older product)

If it is, it's not worth saving 5$...

The TeamGroup CX2 1 TB SSD is one of their latest but it is a no frills SSD which is why it's the cheapest you'll find anywhere. Based on their spec sheet, there isn't DRAM but there is an SLC cache. The Samsung QVO by comparison has a DRAM and SLC cache. From reviews I read online, SSDs with solely an SLC cache still aren't as good as ones with DRAM. But this is really the first time I've ever taken DRAM vs DRAM-less into consideration when getting an SSD

[SquintyG33Rs]

4 minutes ago, Bombastinator said:

Yes.  That is what I was saying.  There’s also lower latency, but again, SSDs are still way way faster than HDDs that way.  Getting into those fractional differences again. 

not when it becomes slower than HDD

[Bombastinator]

2 minutes ago, SquintyG33Rs said:

no under sequential writes the DRAM will make a difference and the performance will crumble on the cacheless drive much faster.

actually a cache-less drive becomes unbearably slow once it's filled up because it was using free space as cache and it can't do that anymore. for eveyrday windows if you never use more than 80% capacity it probably won't show a difference but once full the cache-less drive is slower than HDD while the Samsung would still do pretty good.

I have yet to see an SSD get that slow, but we seem to be arguing to the same purpose.  My statement was apparently there are some cacheless SSDs that can use system ram as cache.  Someone mentioned that this was a sata drive though so that sort of thing might not work, in which case you’re talking about a cacheless drive that can’t use system ram at all, so yeah.  They’re terrible. 

[Generalkidd]

2 minutes ago, Bombastinator said:

Yes.  That is what I was saying.  There’s also lower latency, but again, SSDs are still way way faster than HDDs that way.  Getting into those fractional differences again. 

Well the main concern people have with QLC SSDs is that once you use up the cache (especially if there's no DRAM cache either), the actual speeds of QLC SSDs when writing directly to it is actually slower than a decent HDD. That's why it's often recommended to get an SSD with DRAM. But in my case, between the 2 options I had, the only SSD with DRAM would've been the QLC option. TLC memory gets about as slow as hard drives too when you use up their cache but not as slow as QLC which is like as bad as a 5400 RPM HDD. So basically I wasn't sure if it was better to go with "faster memory but no DRAM cache" or "slowest memory but good DRAM cache". I ended up choosing the latter but was curious if I made the right choice. 

[Bombastinator]

18 minutes ago, Generalkidd said:

Well the main concern people have with QLC SSDs is that once you use up the cache (especially if there's no DRAM cache either), the actual speeds of QLC SSDs when writing directly to it is actually slower than a decent HDD. That's why it's often recommended to get an SSD with DRAM. But in my case, between the 2 options I had, the only SSD with DRAM would've been the QLC option. TLC memory gets about as slow as hard drives too when you use up their cache but not as slow as QLC which is like as bad as a 5400 RPM HDD. So basically I wasn't sure if it was better to go with "faster memory but no DRAM cache" or "slowest memory but good DRAM cache". I ended up choosing the latter but was curious if I made the right choice. 

I think you did as the answer for both of these seems to be “try real hard not to run out of cache” my memory is lack of cache also affects longevity. Also, even if QLC is slower than TLV when both have enough cache it won’t matter since both are faster than sata3

[Blue4130]

2 hours ago, Bombastinator said:

. Also, even if QLC is slower than TLV when both have enough cache it won’t matter since both are faster than sata3

Do a large transfer that exceeds the cache, you'll see very quickly that it isn't faster than sata 3. Speeds can drop to double digits. 

[Bombastinator]

1 hour ago, Blue4130 said:

Do a large transfer that exceeds the cache, you'll see very quickly that it isn't faster than sata 3. Speeds can drop to double digits. 

Ew.  Good to know.  So the bigger the cache the less often it happens.  HDDs have had cache forever though.  If SSDs without cache were actually slower than HDDs without cache, then how would they be faster?  

[Blue4130]

2 hours ago, Bombastinator said:

Ew.  Good to know.  So the bigger the cache the less often it happens.  HDDs have had cache forever though.  If SSDs without cache were actually slower than HDDs without cache, then how would they be faster?  

Don't look at some random peak number. Look at sustained transfer. Here's an example... 

 

It may peak at over 400, but it doesn't last lomg... 

[mariushm]

Get a TLC drive.

 

The DRAM presence only really matters when you write LOTS of data or LOTS of very small files to the SSD. Having DRAM makes a SSD a bit faster when you're doing that. It doesn't really make a difference when reading files. 

 

In contrast TLC or QLC is a significant performance difference, and a significant endurance difference. 

 

The DRAM is used by a SSD to keep track of where data is stored in the memory chips (ex first megabyte of file xyz.txt is stored in memory chip 2, next megabyte is stored in chip 4 and so on).  Every time you write a file, or change something in a file, the SSD controller has to update that list.

If your SSD has no DRAM, after every write to a memory chip, it has to go and do another write to update the list which is stored in a hidden area of your SSD. 

If your SSD has DRAM, the list is copied in DRAM when the SSD turns on, and as you write things the list is updated in the RAM, and the SSD controller backs up the content from DRAM to that list stored in the hidden area periodically (so that if there's a power loss, the changes kept in DRAM aren't lost)

 

So if you have lots of very small writes, a SSD without DRAM may get a performance hit, because it would have to constantly pause and update the internal list. 

 

There are SSDs without DRAM but which take advantage of  HMB (host memory buffer or whatever) - basically, the SSD controller doesn't have 512 MB or 1 GB of DRAM to copy the whole internal list of files in the DRAM, but it can "burrow" a small amount of ram from the computer for some help. 

For example, the SSD controller can reserve 64 MB of memory and as you write stuff to the SSD, the SSD can read a 64 MB portion of that internal list that keeps track of where files are stored, put this 64 MB into the computer RAM, and as you write stuff the controller updates the portion in RAM, and when a significant time has passed it writes this 64 MB portion of memory back into the SSD.

So,  a SSD without DRAM but with ability to borrow RAM from computer can have a write performance somewhere in-between DRAM and no-DRAM SSD. 

 

TLC has higher endurance and higher write speeds.  

QLC has lower endurance and low write speeds. 

 

SSDs  "cheat" by using a portion of the memory in pseudo-SLC mode - instead of writing 3 bits into each TLC memory cell, or 4 bits into each QLC memory cell, they put only 1 bit in each cell to obtain very fast write speeds. 

So for example, let's say you have a SSD that has 500 GB of free disk space.  The SSD controller can "take" 300 GB of TLC memory or 400 GB of QLC memory and creates an internal write cache of 100 GB of "pseudo-SLC" memory and whatever data comes into the drive is written very fast in this 100 GB of memory. 

When you stop writing data into the drive, the controller slowly copies data out from this very fast portion of memory into the slower TLC or QLC memory. 

 

The maximum amount of SLC cache varies depending on free disk space - if your 500 GB free space drops to 200 GB of disk space for example, the SSD controller may only use 100-150 GB of that for SLC mode cache ... and that's 1/3 or 1/4 of the amount or around 30 GB SLC mode for a TLC drive,  or around 20 GB of SLC mode memory for a QLC drive. 

 

It also varies from controller to controller ... for example WD SN550 and WD SN750 have a fixed 12 GB SLC cache no matter the free capacity, while Samsung 980 has up to around 120-160 GB if my memory is correct. 

 

So this is how you get 2-3 GB/s of write speeds... as long as that SLC-mode buffer isn't filled, you get fast speeds.

If you manage to write more than the amount of SLC mode memory, your speeds will go down, because the controller has to write data directly into TLC or QLC memory.  

When writing to TLC memory, you may get as low as 200-500 MB/s write speeds, but with QLC it can be as low as 20-60 MB/s 

 

 

[Bombastinator]

5 hours ago, mariushm said:

Get a TLC drive.

 

The DRAM presence only really matters when you write LOTS of data or LOTS of very small files to the SSD. Having DRAM makes a SSD a bit faster when you're doing that. It doesn't really make a difference when reading files. 

 

In contrast TLC or QLC is a significant performance difference, and a significant endurance difference. 

 

The DRAM is used by a SSD to keep track of where data is stored in the memory chips (ex first megabyte of file xyz.txt is stored in memory chip 2, next megabyte is stored in chip 4 and so on).  Every time you write a file, or change something in a file, the SSD controller has to update that list.

If your SSD has no DRAM, after every write to a memory chip, it has to go and do another write to update the list which is stored in a hidden area of your SSD. 

If your SSD has DRAM, the list is copied in DRAM when the SSD turns on, and as you write things the list is updated in the RAM, and the SSD controller backs up the content from DRAM to that list stored in the hidden area periodically (so that if there's a power loss, the changes kept in DRAM aren't lost)

 

So if you have lots of very small writes, a SSD without DRAM may get a performance hit, because it would have to constantly pause and update the internal list. 

 

There are SSDs without DRAM but which take advantage of  HMB (host memory buffer or whatever) - basically, the SSD controller doesn't have 512 MB or 1 GB of DRAM to copy the whole internal list of files in the DRAM, but it can "burrow" a small amount of ram from the computer for some help. 

For example, the SSD controller can reserve 64 MB of memory and as you write stuff to the SSD, the SSD can read a 64 MB portion of that internal list that keeps track of where files are stored, put this 64 MB into the computer RAM, and as you write stuff the controller updates the portion in RAM, and when a significant time has passed it writes this 64 MB portion of memory back into the SSD.

So,  a SSD without DRAM but with ability to borrow RAM from computer can have a write performance somewhere in-between DRAM and no-DRAM SSD. 

 

TLC has higher endurance and higher write speeds.  

QLC has lower endurance and low write speeds. 

 

SSDs  "cheat" by using a portion of the memory in pseudo-SLC mode - instead of writing 3 bits into each TLC memory cell, or 4 bits into each QLC memory cell, they put only 1 bit in each cell to obtain very fast write speeds. 

So for example, let's say you have a SSD that has 500 GB of free disk space.  The SSD controller can "take" 300 GB of TLC memory or 400 GB of QLC memory and creates an internal write cache of 100 GB of "pseudo-SLC" memory and whatever data comes into the drive is written very fast in this 100 GB of memory. 

When you stop writing data into the drive, the controller slowly copies data out from this very fast portion of memory into the slower TLC or QLC memory. 

 

The maximum amount of SLC cache varies depending on free disk space - if your 500 GB free space drops to 200 GB of disk space for example, the SSD controller may only use 100-150 GB of that for SLC mode cache ... and that's 1/3 or 1/4 of the amount or around 30 GB SLC mode for a TLC drive,  or around 20 GB of SLC mode memory for a QLC drive. 

 

It also varies from controller to controller ... for example WD SN550 and WD SN750 have a fixed 12 GB SLC cache no matter the free capacity, while Samsung 980 has up to around 120-160 GB if my memory is correct. 

 

So this is how you get 2-3 GB/s of write speeds... as long as that SLC-mode buffer isn't filled, you get fast speeds.

If you manage to write more than the amount of SLC mode memory, your speeds will go down, because the controller has to write data directly into TLC or QLC memory.  

When writing to TLC memory, you may get as low as 200-500 MB/s write speeds, but with QLC it can be as low as 20-60 MB/s 

 

 

 

The cache allows the ssd to do better wear leveling and take less wear from housekeeping.  That a qlc without cache is inferior to a TLC without cache is axiomatic.  The question is a qlc with cache vs a tlc without cash?  Can the hmb (thanks, couldn’t remember the acronym) work over sata3? Sata3 isn’t very fast, compared to m key nvme.  Also there are some cacheless drives with no hmb.  Are they an issue?  If hmb works over sata3 and is ubiquitous I would have to agree.

Edited February 24, 2022 by Bombastinator

[mariushm]

HMB (host memory buffer) is part of pci-e specification, so naturally there's no such thing in SATA 

 

Like I said, the DRAM cache is mostly used to keep that translation table in RAM and minimize the writes caused by updating this translation table. 

Think of the translation table as a 1 GB file (about this much is required for a 1 TB drive) that's stored in a hidden portion of Flash memory just like a regular file.

 

If you write a big file the controller can push high speeds and dump this incoming data into the SLC cache area, but from time to time it would have to pause and update the hidden translation table file because the SSD doesn't have enough capacitors or built in batteries to successfully update this translation table while power is lost. 

If you have DRAM cache, the SSD controller can update the translation table in memory and if there's a power loss, it can dump the modified chunks of ram into a hidden area. After a reboot, the controller checks that dump and incorporates the changes into the file translation table. 

It also periodically logs the changes to the translation table on the SSD but with the dram cache it can combine multiple updates into a single larger update which results in less pauses. 

 

 

The wear on the SSD due to constantly updating that translation table file on the SSD is not a big deal, because DRAM drives also have to periodically update that file, so they also cause some amount of wear, just less. 

The SSD controller could also keep that translation file in a portion of the flash memory that's in SLC mode, for high speeds, high endurance and higher erase count (SLC memory can do 10k+ erases, MLC goes down to around 4-6k, TLC to around 3-4k, QLC goes down to 500-800 erases) so you just don't know how much extra wear you would have without dram. 

 

I'd take a TLC without DRAM over a QLC with DRAM anytime.  DRAM benefits are very overblown, exaggerated.  The average user would NOT really notice a SSD with DRAM being faster while installing a game, while downloading something, while launching a game level... 

Would maybe notice if they update a 100 GB database, if they compile Google Chrome or some similarly big project  (due to lots of small binary files being generated and due to the compiler doing things in parallel, so lots of IOPS) 

 

On a SATA SSD, if they use good TLC or MLC flash memory, you don't have enough bandwidth (540 MB/s max write speed) to actually see a DRAM chip give better performance.  Unfortunately, a lot of SATA SSDs are mostly made with cheap or lower grade flash memory chip (chips with lots of faulty areas) 

 

 

[SSD Sean]

Don’t get a DRAM-less SATA SSD. They are garbage…you can also take my word for it as I’m a world leading SSD reviewer.