1. Technology for Backbone Web Caching Peter B Danzig Network Appliance November 1998

2. Speakers Peter Danzig -- Network Appliance “Scaling Cache Deployments” Shirish Sathaye -- Alteon Networks “Scaling w/L4-Switches” James Aviani -- Cisco “Scaling WCCP” Bill Maggs -- MCI/Worldcomm “Routing and Caching” Ed Kern Digex “Report on Digex cache deployment”

3. Rules of thumb for Scaling Individual Cache Nodes Peter B Danzig Network Appliance November 1998

4. Scaling Individual Cache Nodes • Rule of thumb resources required per megabit • Simultaneous TCP Connections 500 • Disk Needed 4 GB • Disk Arms Needed 1/2-1/3 • Memory 32 MB

5. Simultaneous Connections Little’s Law: N = l W W: Average time to fetch a web page: 4-10 Seconds l: URLs/Second: 25 per megabit N: Number of TCP connections N = 2 * 25 * 10 = 500 connections/megabit

6. Disk Arms Keep disks below 50% busy A cache behind a cache sees random references Assume all references require 1 disk/ops Depending on OS, a single disk can achieve 50-200 operations per second Per megabit: 25 ops/S * 2 (for head room) yields anywhere from 1 disk to 1/4 disk per megabit

7. Disk Space A megabit link can draw 9GB/day Peak to average load is about 4X So a 9GB disk holds the entire reference set of 4-days of operation. Assume 1/2 of references are already cached or are non-cachable…. Use 4GB of disk per megabit

8. Memory Each megabit means 500, dual 8 KB TCP buffers: 8 MB Proxy state for 500 connections @ 32KB: 16 MB Disk buffer pool: 8MB Leads to 32MB/megabit

9. CPU • Depends on the manufacturer and OS release • For example: • C720 running NetCache-3.3: 25 mbits/s • C760 running NetCache-3.3: 37 mbits/s

10. Aggregating Cache Nodes • Currently have two technologies for clustering cahe nodes • L4 Switches • Alteon, Arrowpoint, Foundry, and RND • WCCP • Cisco routers and WCCP licensees