When is dram recommended?

[NAMAJAFF]

I got a Samsung 980pro for my boot device and I'm wondering if I could just buy an ssd like this that's cheap and pretty big but has no dram. 

 

Is it even worth it or should I just stick with hard drives? 

[mariushm]

Your link goes to this page.

 

To answer the question, DRAM on SSDs is not needed or required, DRAM helps mostly when you have programs that use the drive heavily, reading or writing lots of files in parallel, overwriting lots of chunks in files etc etc

It practically doesn't help with reading files faster, it isn't used to cache writes so it won't make the SSD write files faster to its flash memory.

Modern SSDs can also take advantage of HMB, basically they can "borrow" a chunk of ram from the computer (usually 32-64MB of memory) that they can interact with through pci-e, and that ram can used similarly how DRAM would normally was used, to improve performance at heavy IO  (which again, rarely happens for a regular home user that loads windows and some games, such things are not heavy IO)

 

Can't say to buy what you see as cheap and pretty big because there are some SSDs I don't like recommending (for example QLC based drives - don't feel like it's worth buying QLC when you can play 10-20% more to get TLC based drives which are better) or maybe you have initially linked to some sata only or even worse, some eMMC drive.

 

[WereCat]

DRAM on SSDs is used as a cache. A DRAM-less SSD will use the SLC NAND as a cache.

 

The difference is that once you fill the SLC cache on a DRAM-less SSD (usually by copying large files) the performance will drop so much that it may actually end up being slower than a HDD.

The size of SLC-cahce on a DRAM-less SSDs typically scales with the capacity of the SSD so a 2TB SSD will have bigger cache and sustain it's speed for longer than a 512GB DRAM-less SSD.

 

The DRAM cache on SSD is many times faster and the performance drop will be there too, but nowhere near to that extent.

[leclod]

I have my OS on a QLC drive since 2019 (probably DRAM-less too (Oh No, it's not DRAM-less )). Everything green so far.

I honestly wonder if I'd see a difference with one of the fast drives.

[mariushm]

35 minutes ago, WereCat said:

DRAM on SSDs is used as a cache. A DRAM-less SSD will use the SLC NAND as a cache.

 

No, it's not.  It's basically used to hold the translation table, a table which holds information about where the data is actually located in the flash memory chips.

The SSD controller copies the translation table from flash to DRAM at boot and then uses the DRAM to save one read from the flash memory chips (reading from ram is faster than reading from flash memory) and as a write cache for the modifications to this translation table, and periodically it will dump to flash memory chips the modifications to this translation table (so that you don't lose data at power loss or sudden reboots)

This means when you get improved performance if you read and write LOTS and LOTS of stuff at same time. If you use it like a normal drive, the performance of the regular flash memory chips  AND the HMB features AND the small internal caches inside the controller (a few MB at most) are enough.

 

more detailed

 

The operating system seems the storage device as a chain of sectors, each 512 or 4096 bytes in size (most common sizes) so a file can be stored in multiple segments ex  sectors 500 to 2000, then sectors  5000 to 10000

When an operating system requests a file, it asks the SSD to read sectors 500 to 2000 , then read sectors 5000 to 10000. The SSD controller has no idea if that's a file or not, and doesn't care.

 

The SSD uses a table which simply says "sector  500 is stored in flash memory 3, block 100, page 5" , sector 501 is located in flash memory chip 4, block 10, page 200"  and so on.

A block is a group of pages, typically 24-32 MB in size, and a page is 512 - 4096 bytes (so a block could have for example 65536 pages x 512 bytes per page = 32 MB block)

 

Each time you read something from a SSD, the SSD controller has to look up where the sectors are stored, then request the data from individual flash memory chips and compose it back into a stream of data to be given to the operating system.

 

Just the same, when data is written to the SSD, the operating  system just says "write these 512 bytes in sector 500" but the SSD controller can't do that, because flash memory doesn't work like that.

In Flash memory, you can't erase individual sectors (the "pages") to write data into them, you have to erase the whole block and that causes a minor damage to that block - depending on memory type you get a different amount of erases before the block becomes unreliable, not thrustworty. For MLC that's 6000-10000 erases, for TLC it's around 3-5000, for QLC it's 200-1000 erases.

So instead, the SSD controller looks up in the table where that sector is and puts a mark there "this page can be erased at some point in the future, it contains old data". Then, it finds a writable page in some other memory chip, puts the new data there and updates the translation table to say  "sector 500 is now at memory chip x , block y , page z

 

In background at some point in the future, the SSD controller will try to find blocks with a large majority of pages marked as "can be erased", and will copy the remaining pages with valid data to other memory chips and erase the whole block, putting back the whole block into operation.

 

The pSLC  (pseudo-SLC) is large portions of the free flash memory "switched" into a SLC mode, where instead of writing 3 or 4 bits into each cell, only 1 bit is written, just like it would have worked with actual SLC memory. In this mode, it's easier to do erases, so memory in this mode can tolerate more erases, like 10k or more... and you also get much faster write speeds.

 

When writing stuff to the SSD, the SSD controller will put in that translation table the location of the sector in the SLC write cache and later when it moves the data from the write cache to permanent flash memory (TLC or QLC) it has to update the translation table again.

 

So for example if you have a 1 TB Crucial P3 drive, that drive uses QLC memory chips and can use ALL its memory chips as pseudo-SLC - if the drive is completely empty, it will behave like having a 250 GB pSLC write cache (because QLC stores 4 bits per cell, but SLC stores only 1 bit, so you get 1/4 of capacity as SLC cache)

If you copy 50 GB to the SSD, those 50 GB will be written fast, and a few minutes later once the transfer is done, in the background the SSD controller will convert some of the memory to QLC. Now, you have 50 GB used and only 950 GB free, which means you'll have only 950 / 4 = ~ 235 GB of pSLC write cache.

Crucial P3 is an exception - most drives go up to around 100-160 GB per TB of pSLC cache and can't use whole capacity as SLC write cache.

 

 

 

 

 

[leclod]

3 hours ago, mariushm said:

In Flash memory, you can't erase individual sectors (the "pages") to write data into them, you have to erase the whole block and that causes a minor damage to that block - depending on memory type you get a different amount of erases before the block becomes unreliable, not thrustworty. For MLC that's 6000-10000 erases, for TLC it's around 3-5000, for QLC it's 200-1000 erases.

200 erases sounds like not a lot. Consistent with the 400TBW rating of my 2TB 660p. I'm still at 97% health with 53TB written though, I should be at 86%.

[NAMAJAFF]

10 hours ago, mariushm said:

Your link goes to this page.

 

To answer the question, DRAM on SSDs is not needed or required, DRAM helps mostly when you have programs that use the drive heavily, reading or writing lots of files in parallel, overwriting lots of chunks in files etc etc

It practically doesn't help with reading files faster, it isn't used to cache writes so it won't make the SSD write files faster to its flash memory.

Modern SSDs can also take advantage of HMB, basically they can "borrow" a chunk of ram from the computer (usually 32-64MB of memory) that they can interact with through pci-e, and that ram can used similarly how DRAM would normally was used, to improve performance at heavy IO  (which again, rarely happens for a regular home user that loads windows and some games, such things are not heavy IO)

 

Can't say to buy what you see as cheap and pretty big because there are some SSDs I don't like recommending (for example QLC based drives - don't feel like it's worth buying QLC when you can play 10-20% more to get TLC based drives which are better) or maybe you have initially linked to some sata only or even worse, some eMMC drive.

 

thanks!

 

10 hours ago, mariushm said:

Your link goes to this page.

 

To answer the question, DRAM on SSDs is not needed or required, DRAM helps mostly when you have programs that use the drive heavily, reading or writing lots of files in parallel, overwriting lots of chunks in files etc etc

It practically doesn't help with reading files faster, it isn't used to cache writes so it won't make the SSD write files faster to its flash memory.

Modern SSDs can also take advantage of HMB, basically they can "borrow" a chunk of ram from the computer (usually 32-64MB of memory) that they can interact with through pci-e, and that ram can used similarly how DRAM would normally was used, to improve performance at heavy IO  (which again, rarely happens for a regular home user that loads windows and some games, such things are not heavy IO)

 

Can't say to buy what you see as cheap and pretty big because there are some SSDs I don't like recommending (for example QLC based drives - don't feel like it's worth buying QLC when you can play 10-20% more to get TLC based drives which are better) or maybe you have initially linked to some sata only or even worse, some eMMC drive.

 

sorry i messed the link up the ssd i was talking about was the PNY CS2140 2TB M.2 NVMe Gen4 it doesnt have dram but it does support HMB

[mariushm]

Well, it looks ok... but don't buy it just because it's pci-e 4.0 because the maximum speeds are 3.3 GB/s read , and 3 GB/s write speeds ... speeds that a pci-e 3.0 ssd can do.

 

I think it would be comparable with HP EX900 Plus (but which advertises only 800 TBW, not 1200 TBW, but could just be HP is more honest, less optimistic) : https://www.amazon.com/HP-EX900-Plus-2TB-NVMe/dp/B09CG7SM5K/

 

If you want something more trustworthy, go for Samsung 970 Evo Plus which is now $156 : https://www.amazon.com/Samsung-970-EVO-Plus-MZ-V7S2T0B/dp/B07MFZXR1B/

After this, another solid choice would be WD SN570 at $158 : https://www.amazon.com/Western-Digital-SN570-Internal-Solid/dp/B09JM8DJNS/

 

WD SN570 has a lower SLC cache amount but otherwise it's about the same read and write speeds wise and endurance.

 

[NAMAJAFF]

51 minutes ago, mariushm said:

Well, it looks ok... but don't buy it just because it's pci-e 4.0 because the maximum speeds are 3.3 GB/s read , and 3 GB/s write speeds ... speeds that a pci-e 3.0 ssd can do.

 

I think it would be comparable with HP EX900 Plus (but which advertises only 800 TBW, not 1200 TBW, but could just be HP is more honest, less optimistic) : https://www.amazon.com/HP-EX900-Plus-2TB-NVMe/dp/B09CG7SM5K/

 

If you want something more trustworthy, go for Samsung 970 Evo Plus which is now $156 : https://www.amazon.com/Samsung-970-EVO-Plus-MZ-V7S2T0B/dp/B07MFZXR1B/

After this, another solid choice would be WD SN570 at $158 : https://www.amazon.com/Western-Digital-SN570-Internal-Solid/dp/B09JM8DJNS/

 

WD SN570 has a lower SLC cache amount but otherwise it's about the same read and write speeds wise and endurance.

 

whats your opinion on the Kingston nv2? 

 

sorry if im bothering you but it looks like the best choice for my budget and i wanted your opinion.

 

its slower in write speeds than the pny but it shouldnt matter much for gaming