5.4.2. I/O Loads and Performance
5.4.2. I/O Loads and Performance The other thing that controls hard drive performance is the I/O load to which a hard drive is subjected. Some of the specific aspects of the I/O load are: The amount of reads versus writes The number of current readers/writers The locality of reads/writes These are discussed in more detail in the following sections. 5.4.2.1. Reads Versus Writes For the average hard drive using magnetic media for data storage, the number of read I/O operations versus the number of write I/O operations is not of much concern, as reading and writing data take the same amount of time [19] . However, other mass storage technologies take different amounts of time to process reads and writes [20] . The impact of this is that devices that take longer to process write I/O operations (for example) are able to handle fewer write I/Os than read I/Os. Looked at another way, a write I/O consumes more of the device's ability to process I/O requests than does a read I/O. [19] Actually, this is not entirely true. All hard drives include some amount of on-board cache memory that is used to improve read performance. However, any I/O request to read data must eventually be satisfied by physically reading the data from the storage medium. This means that, while cache may alleviate read I/O performance problems, it can never totally eliminate the time required to physically read the data from the storage medium. [20] Some optical disk drives exhibit this behavior, due to the physical constraints of the technologies used to implement optical data storage.