David Malan teaching CS75 lecture 9, Scalability

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　　https://youtu.be/-W9F__D3oY4
　　Storage
　　PATA, SATA, SAS (15,000 rpm), SSD,
　　RAID0 : striping, double throughput / size, no redundancy; RAID1 : mirror; RAID2 : bit-level striping with parity, not used today; RAID3 : bit-level striping with dedicated parity drive, not used today; RAID4 : block-level striping with dedicated parity ; RAID5 : block-level striping with dedicated parity, single drive failure tolerance; RAID6 : block-level striping with double parity, two drive failure tolerance
　　NAS, a file server, accessed through NFS, SMB etc.
　　SAN, a virtual disk, accessed through iSCSI, Fiber Channel etc.
　　Vertical scaling
　　Horizontal scaling
　　DNS round-robin load balancing, heavy vs. light requests
　　load balancer
　　Software-based LB: ELB, HAProxy, LVS etc.
　　Hardware-based : F5, Cisco, Citrix etc.
　　cookie/session affinity (sticky session)
　　separate session server (e.g. a redis or MySQL server for hash table)
　　LB inserts cookie content to remember backend-id
　　this is standard approach actually nowadays, AWS ELB (Elastic Load Balancer) provides this feature as service, http://docs.aws.amazon.com/elasticloadbalancing/latest/classic/elb-sticky-sessions.html, for example, you can specify a cookie name which will drive the distribution of requests.
　　Caching
　　DNS cache
　　MySQL Query Cache
　　memcached
　　Database Replication
　　master / slave : and you can make master write-only, and slaves obviously read-only
　　master / master - slave set up
　　Database Partitioning
　　mit.facebook.com.
　　LB, cross data center, geolocation distribution