14. describe some advantages and disadvantages of using ssds as a caching tier and as a disk-drive replacement compared with using only hard disks.

SSDs have the advantage of being faster than magnetic disks as there are no moving parts and therefore do not have seek time or rotational latency. They have the same characteristics as magnetic hard disks, but can be more reliable. The disadvantage is that they are generally more expensive per megabyte than traditional hard disks.