Q50

A file system uses an in-memory cache to cache disk blocks. The miss rate of the cache is shown in the figure. The latency to read a block from the cache is $1$ ms and to read a block from the disk is $10$ ms. Assume that the cost of checking whether a block exists in the cache is negligible. Available cache sizes are in multiples of $10$ MB.

The smallest cache size required to ensure an average read latency of less than $6$ ms is _________ MB.