It's read as well as write IOPS and seek time. The Ethereum state database uses hashes as keys and is larger than anyone's reasonable amount of RAM. So most acc

It's read as well as write IOPS and seek time. The Ethereum state database uses hashes as keys and is larger than anyone's reasonable amount of RAM. So most accesses are all over the database in terms of physical location, and it can't be cached in RAM effectively. There is various work to improve this, but the basic architecture does depend on random access storage to a great extent.