SSD's are quirky in the way they write and erase data. Data is stored in groups called "pages". Pages are finite in size and can only be written to when empty. Therefore, in order to write to a page that already contains data, it must first be erased. This would be simple, except each page belongs to a group called a "block". While data is written in pages, it can only be erased with its entire block. So, when the SSD wants to reuse an existing, no longer valid page, the other (valid) pages in the block must be copied into cache (or memory on the controller) while the entire block is erased. The SSD then rewrites the entire set of valid data, old and new. Furthermore, as SSD's become full, they are forced to spread data over many, disparate cells. When reading the data, the SSD must address all of these cells simultaneously. These processes take time, which is perceived as decreased performance.
This is why Over Provisioning, which guarantees a certain amount of free swap space to use for Garbage Collection, is so important for SSD performance ？ it allows free space to be prepared in advance through data consolidation.
Note: The performance of Samsung SSDs can be checked by using Samsung SSD Magician tool available at samsung.com/us/support. The benchmarking feature of Samsung SSD Magician uses the IOMeter tool. There are also a number of 3rd party tools available, such as CrystalDiskMark and PCMark that may be used. Performance results may vary depending on which benchmarking tool is used.
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