Department of Electronics Advanced Information Storage 18 Atsufumi Hirohata 17:00 05/December/2013 Thursday (P/T 006)

Quick Review over the Last Lecture Millipede memory : * * Nano-RAM : Floating junction gate :

18 RAID and Cloud Computing Cloud computing Storage technology RAID Parity error detection Data striping Data mirroring

Cloud Computing * In 2006, Eric E. Schmidt (Google) first introduced the phrase : *

Cloud Layers * Cloud computing extends the existing concepts : * SaaS : Software as a service PaaS : Platform as a service IaaS : Infrastructure as a service

Cloud Companies *

Cloud for Mobile Devices Mobile data are stored in servers in cloud : * * iPhones 1 server in cloud Can store data from 8 iPads

Storage Technology In 1987, David Patterson, Garth A. Gibson and Randy Katz defined : * * ** Redundant array of inexpensive (independent) disks (RAID) combines multiple disk drive components into a logic unit Data distributed across the drives Levels of redundancy and performance required → RAID 0 ~ 10

RAID 0 * Block-level striping without parity or mirroring : * Minimum number of drives : 2 Space efficiency : 1 Fault tolerance : 0 Array failure rate : 1 – (1 – r) n Read performance : nX Write performance : nX

Parity Error Detection * Parity bit is used for error detection : * Even / odd parity Binary stream contains even / odd number of “1”. For example, serial data transfer uses Binary stream : 7 digit + Parity : 1 digit

Data Striping * Data stream is distributed to several drives : *

RAID 1 * Mirroring without parity or striping : * Minimum number of drives : 2 Space efficiency : 1 / n Fault tolerance : n – 1 Array failure rate : r n Read performance : nX Write performance : 1X

Data Mirroring * Data are duplicated onto another drive(s) : *

RAID 2 * Bit-level striping with dedicated Hamming code parity : * Minimum number of drives : 3 Space efficiency : 1 – 1 / n log 2 (n – 1) Fault tolerance : 1 drive depending on the corresponding data and parity conditions Array failure rate : variable Read performance : variable Write performance : variable

RAID 3 * Bit-level striping with dedicated parity : * Minimum number of drives : 3 Space efficiency : 1 – 1 / n Fault tolerance : 1 drive Array failure rate : 1 – (1 – r) (n – 2) / 2 Read performance : (n – 1 )X Write performance : (n – 1 )X

RAID 4 * Block-level striping with dedicated parity : * Minimum number of drives : 3 Space efficiency : 1 – 1 / n Fault tolerance : 1 device Array failure rate : 1 – (1 – r) (n – 2) / 2 Read performance : (n – 1)X Write performance : (n – 1)X

RAID 5 * Block-level striping with dedicated parity : * Minimum number of drives : 3 Space efficiency : 1 – 1 / n Fault tolerance : 1 device Array failure rate : 1 – (1 – r) (n – 2) / 2 Read performance : (n – 1)X Write performance : (n – 1)X

RAID 6 * Block-level striping with double-distributed parity : * Minimum number of drives : 4 Space efficiency : 1 – 2 / n Fault tolerance : 2 device Array failure rate : 1 – (1 – r) (n – 3) / 2 Read performance : (n – 2)X Write performance : (n – 2)X

RAID 10 * Mirroring without parity and block-level striping : * Minimum number of drives : 4 Space efficiency : 2 / n Fault tolerance : 1 device Array failure rate : Read performance : nX Write performance : (n / 2)X