75

I was reading this Tom's Hardware article on testing SSDs and came across the following claim:

With SSDs, performance varies by capacity point. Smaller drives tend to be slower than larger ones, even in the same family.

However, the article doesn't backup this claim or explain why.

It doesn't seem intuitive to me that smaller drives would be slower. I would think it would be the other way around since a larger drive has a wider "area" to access via the same bandwidth.

So is it true that smaller (capacity) SSDs are slower? And if so, why?

Improve this question
4
  • 9
    'Smaller' might just be 'older design'
    – Aganju
    Apr 2, 2016 at 16:44
  • 7
    By "small", do you mean in physical size or in capacity?
    – JesseTG
    Apr 3, 2016 at 4:04
  • 1
    @JesseTG Capacity. I'll make that clearer.
    – PGmath
    Apr 3, 2016 at 4:05
  • 2
    The crux of the issue is that you're reasoning about throughput using a latency argument.
    – user541686
    Apr 3, 2016 at 8:37

3 Answers 3

Reset to default
109

Larger SSDs from the same SSD model/family (comparing different models makes no sense) are faster when writing data because they use more Channels in parallel:

enter image description here

while smaller ones only use few channel (4 instead of 8) because they have less NAND modules on it.

Improve this answer
6
  • 13
    I'd add "for a given family/controller" if I wanted to be pedantic.
    – Journeyman Geek ♦
    Apr 3, 2016 at 7:50
  • 8
    Worth pointing out that the reason for this is that flash chips only tend to be available at a reasonable price in one or two capacities at a time. For instance, currently MLC chips are available in 32, 64 and 128 gigabit varieties, and as the 64 gigabit chips only cost slightly more than 32 gigabit ones but less than half the 128s, anyone designing a new SSD range today will probably design it based on 64Gb chips, regardless of the capacity they're aiming for.
    – Jules
    Apr 4, 2016 at 12:40
  • Now that's a good simple answer!
    – Raystafarian
    Apr 7, 2016 at 8:24
  • @magicandre1981 Would you be willing to write a bit more about this as an article for the SU Blog?
    – undo
    Apr 10, 2016 at 17:58
  • @RahulBasu not really.
    – magicandre1981
    Apr 10, 2016 at 18:07
54

The higher capacity variants of an SSD model often get their higher capacity from simply having more NAND flash chips of the same type as the lower capacity variants.

Having more flash chips allows for a design where the controller on the SSD can access more data in parallel, allowing for higher speeds.

Improve this answer
1
  • 39
    Sort of like a built-in RAID-0.
    – kasperd
    Apr 3, 2016 at 9:36
5

Let's pretend that SSD is using 32GB NAND chips for storage, so an 128G SSD need 4 of those chips to add up the space, and an 256G need 8 of the identical chips to make up the space, which means for read/write, on the 256G SSD it can R/W to 8 chips together rather than 128G's 4 chips, which make it much faster.

But since there are other bottle necks, the final speed won't show as double on both R/W, however in real life, there are a lot of examples of how 128G's only have half of the write speed of the 256G's(i.e retina Macbook Pro's PCIe SSD benchmark, Sandisk Extreme CZ80 USB Drive).

The description was not 100% accurate, but it gives the basic idea of why small SSD are slower.

Improve this answer

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .