Distributed System Design - Estimations

Example

Estimate QPS

• 100M active users
• => 10 times a day, each visit may send 10 requests (incl. images, css, etc)
• => 10B requests / day
• => ~100k requests/seconds on average, ~200k requests/second at peak

Estimate Disk Failures

• 200k QPS
• each request 10 disk seeks=>2M disk seeks per second (IOPS)
• each seek 10ms => 100 seeks per second per disk => need 20,000 disks
• 24 disks per machine => 834 machines
• 4 rack unites (RU) per machine, 42 RU rack => 84 racks => 168ft(52m) of rackspace
• disk failure rate per year ~2%
• if you have 1 million, 20k will break every year=>every 1500 seconds a disk breaks