[SOLVED] SSD Layering

wm3797

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When reviews of ssds talk about 96 layer MLC or 128 layer QLC, what does the layer mean? Are the more layers, the better?
 

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Better? IDK for certain about longevity. they allow for higher capacity drives.
REALLY BAD ANALOGY ALERT hopefully you get the general idea.
in a standard SSD the chips are laid out like floor tiles one layer high. in multi-layer chips the layers are like the tiles still in the box sitting on the floor, they are connected through each other rather than connected to each other by the floor, which slows some things down. since the layers are stacked the more layers the higher the capacity for the same area of circuit board. the picture illustrates the 3D way the chips are connected through each other



the MLC means Multi -Level Cell and refers to the ability to store 2 bits of data per cell.
QLC means each cell can hold 4 bits of data.
 

wm3797

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Better? IDK for certain about longevity. they allow for higher capacity drives.
REALLY BAD ANALOGY ALERT hopefully you get the general idea.
in a standard SSD the chips are laid out like floor tiles one layer high. in multi-layer chips the layers are like the tiles still in the box sitting on the floor, they are connected through each other rather than connected to each other by the floor, which slows some things down. since the layers are stacked the more layers the higher the capacity for the same area of circuit board. the picture illustrates the 3D way the chips are connected through each other



the MLC means Multi -Level Cell and refers to the ability to store 2 bits of data per cell.
QLC means each cell can hold 4 bits of data.
Youre right, im lost already. You said layers mean capacity, so does it mean it can hold MORE data ? so 128 layer would be better than 96?
 

R_1

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it gets fuzzy in an apples and oranges way, they cannot be directly compared, one holds twice the data per cell the other does. 2 vs 4. the layering and the levels per cell play a part. assuming each layer holds the same amount of data (4KB per layer MLC vs 4KB per layer QLC), yes the more layers the better.

which drives in particular did you have in mind?
 

wm3797

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it gets fuzzy in an apples and oranges way, they cannot be directly compared, one holds twice the data per cell the other does. 2 vs 4. the layering and the levels per cell play a part. assuming each layer holds the same amount of data (4KB per layer MLC vs 4KB per layer QLC), yes the more layers the better.

which drives in particular did you have in mind?
OH I see. Samsung NVME 970 EVO PLUS vs 970 PRO, both 1 TB each
 

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Check my signature link.

In brief: consider an array like an Excel spreadsheet where you have a column and a row. Add a third vertical direction to that where every plane is a layer. Now add more layers. That's it.

As you add more layers you basically extend a pillar for each column, row combination with every point being a cell that can hold one or more bits (TLC = 3 bits, for example). For the same amount of data this means the cell area can be larger which can be used in a combination of ways: increase performance, increase endurance, increase capacity, etc. There are many secondary or "knock-on" effects to this but that's the basic idea.
 

wm3797

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Check my signature link.

In brief: consider an array like an Excel spreadsheet where you have a column and a row. Add a third vertical direction to that where every plane is a layer. Now add more layers. That's it.

As you add more layers you basically extend a pillar for each column, row combination with every point being a cell that can hold one or more bits (TLC = 3 bits, for example). For the same amount of data this means the cell area can be larger which can be used in a combination of ways: increase performance, increase endurance, increase capacity, etc. There are many secondary or "knock-on" effects to this but that's the basic idea.
OH. Thats the pros. what about the cons to this layering? such as SLC is better than QLC but QLCs are much less expensive
 

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OH. Thats the pros. what about the cons to this layering? such as SLC is better than QLC but QLCs are much less expensive
Don't confuse layers for levels. QLC (quad-level cell) is four bits per cell, SLC (single-level cell) is one bit per cell. Layers are completely different.

The cons to adding more layers is complexity. You may have more bad blocks, higher constraints with etching, etc. Things of that nature. It's now most common to stack multiple blocks together, for example three 32-layer blocks to make a 96-layer structure with what is known as string-stacking. This can reduce yields (more defects) and increase device stress.
 

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