Caching is heavily used in some WSC designs to reduce latency, and there are multiple caching options

Question:

Caching is heavily used in some WSC designs to reduce latency, and there are multiple caching options to satisfy varying access patterns and requirements.

a. Let’s consider the design options for streaming rich media from the Web (e.g., Netflix). First we need to estimate the number of videos, number of encode formats per video, and concurrent viewing users. Assume a streaming video provider that has 12,000 titles for online streaming, each title having at least four encode formats (at 500, 1000, 1600, and 2200 kbps). Let’s also assume that there are 100,000 concurrent viewers for the entire site, and an average video is 75 min long (accounting for both 30-min shows and 2-h videos). Estimate the total storage capacity, I/O and network bandwidths, and video-streaming-related computation requirements.

b. What are the access patterns and reference locality characteristics per user, per video, and across all videos?

c. What movie storage options exist by using DRAM, SSD, and hard drives? Compare them in performance and TCO. Would new memory technologies like those in Problem 6.17 (d) be useful?

Problem 6.17

One trend in high-end servers is toward the inclusion of nonvolatile flash memory in the memory hierarchy, either through solid-state disks (SSDs) or PCI Express-attached cards. Typical SSDs have a bandwidth of 250 MB/s and latency of 75 μs, whereas PCIe cards have a bandwidth of 600 MB/s and latency of 35 μs.

a. Take Figure 6.7 and include these points in the local server hierarchy.

Assuming that identical performance scaling factors like DRAM are accessed at different hierarchy levels, how do these flash memory devices compare when accessed across the rack? Across the array?

b. Discuss some software-based optimizations that can utilize the new level of the memory hierarchy.

c. As discussed in “Fallacies and Pitfalls” replacing all disks with SSDs is not necessarily a cost-effective strategy. Consider a WSC operator that uses it to provide cloud services. Discuss some scenarios where using SSDs or other flash memory would make sense.

d. Recently, some vendors have discussed new memory technologies that are much faster than flash. As an example, look up the specifications for Intel 3D X-point memory and discuss how it would factor in Figure 6.7.

Figure 6.7