Tom's Hardware's Summer Guide: 17 SSDs Rounded Up

Benchmark Results: 4K Random Reads/Writes And Interface Bandwidth

4K random reads are a piece of cake for most SSDs, as reading happens very quickly and flexibly across the flash memory matrix.

Writes, however, can only happen at block size and involve the full read-modify-erase-write cycle. 4 KB writes are very important, as the majority of files on your drive are below 4 KB and file systems are often based on 4 KB blocks. Since SSD block size is way larger than 4 KB, managing lots of 4 KB writes is a worst-case scenario for SSDs. They then have to read-modify-erase-write their full block size, which is a multiple of 4 KB.