Friday, 2 December 2016

Virtualization Oversubscription - What’s so scary? Memory test (8 of 20)

If memory must be copied to or from disk because there is more requested than can be satisfied, what’s the penalty for doing this?


        Memory vs. disk speed is…?

A) Memory is 100x faster than disk

B) Memory is 1,000x faster than disk

C) Memory is 10,000x faster than disk

D) Memory is 100,000x faster than disk

E) Memory is 1,000,000x faster than disk

F) I have no memory of the event, your honour

A modern disk will respond to an I/O in about 5 milliseconds (5 * 1/1000 of a second).  Access to memory is usually in the order of 50 nanoseconds (50 *1/1,000,000,000 of a second).

That makes disk access a hundred thousand (100,000) times SLOWER than memory access. Tiny numbers like this are difficult to comprehend, so imagine that the memory access time was 1 second.  To write something to disk would then take about 27 ¾ hours to complete.

That’s one good reason for avoiding swapping if at all possible! On Monday I'll be looking at vKernel Swap.
In the meantime why not take a look at some of our VMware on-demand webinars and white papers. Join our Community via our Resources section and get free access.
Phil Bell
Consultant