Why smaller SSDs are slower than larger SSDs

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Higher capacity SSDs reliably return better performance numbers than lower capacity drives of the same make and model. If you know nothing about how SSDs work, this seems like a mystery, but the reason behind the slowdown makes a lot of sense.

Larger SSDs have more data channels and DRAM

An SSD consists of NAND memory chips arranged in groups, connected to an SSD controller. The controller is an intelligent device that decides where to physically store the data on the SSD.

With more groups of memory chips, each connected to the controller via a dedicated data bus, the controller can read and write data in parallel. The more clusters you have, the more independent paths there are to move data back and forth. This has an additive effect on performance since each independent memory module can send and receive data without affecting

Smaller units fill faster

SSDs are faster when they are new and relatively empty. This is because an SSD has to erase an entire block of memory cells before writing to it. If all memory cells are empty, the drive simply writes to the empty space. However, if the block is partially full, the drive first has to copy the existing data to a cache, erase the block, and then write to the new empty block.

This adds overhead to drive operations and slows things down. This is why SSDs clear memory blocks in the background that have been marked for deletion and perform “cleanup” to consolidate data, minimizing partially filled memory blocks.

The fuller your SSD is, the fewer empty blocks there are to write to, and larger SSDs are less likely to be as full as smaller drives. This is another reason why smaller drives can degrade in performance more quickly.

There’s more to SSD performance

While having more memory modules in parallel increases performance, this is only one aspect of SSD performance. Memory type affects the fundamental speed at which blocks of memory can be erased and written, so if the two drives you’re comparing also differ in the type of memory modules they use, that has an impact on any difference in memory. performance.

The SSD controller is also absolutely crucial for performance. The intelligence of the controller when it comes to predicting what data to cache or how to shuffle the data to ensure the drive always performs well has significant real-world effects. In other words, the brain of an SSD matters as much as its muscle.

Speaking of caches, larger drives can have proportionally larger cache allocations. The larger a drive’s cache, the faster it will perform when making large transfers or quickly responding to frequent data requests. The same goes for mechanical hard disk drives (HDDs), where two drives that are otherwise identical will perform better on the drive with more cache.

Why not make small SSDs more parallel?

Inevitably, one has to wonder why smaller drives don’t receive the same number of memory modules as larger drives. Just make the modules smaller, right? This would work in theory, but the economic realities of memory production make it a bad idea.

There is a minimum cost below which a memory module cannot be manufactured no matter how low its capacity, because certain aspects of manufacturing are fixed regardless of module capacity. You will see something similar with traditional mechanical drives. There may be no difference in the cost of making a 120 GB and a 250 GB mechanical hard drive, for example. That means no one is going to make the smallest capacity drive.

Memory modules used with smaller SSDs represent the best balance between cost per module and capacity. In other words, a unit with more modules but less capacity per module would cost the same as a larger unit with the same number of modules.