2. ICC Module 3 Lesson 3 – Storage 1 / 6 © 2015 Ph. Janson Information, Computing & Communication Storage – Clip 1 – Principles School of Computer Science & Communications Ph. Janson

3. ICC Module 3 Lesson 3 – Storage 2 / 6 © 2015 Ph. Janson Outline ►Clip 1 – Technology reminder & basic principleClip 1 ►Clip 2 – Storage structuresClip 2 ►Clip 3 – Addressing and namingClip 3 ►Clip 4 – File systemsClip 4 ►Clip 5 – DatabasesClip 5 Intro clipIntro clipPrevious clipNext clipNext clip

4. ICC Module 3 Lesson 3 – Storage 3 / 6 © 2015 Ph. Janson Technology reminder LatencyThroughputCost ($/GB)SizeRetentionAccess RAM1 - 100 nsGB/s10Mo - GoNORandom FlashµsGB/s0.5Go - ToYesRandom Hard disksms100s MB/s0.05> ToYes Random with delay Magnetic tapes Yet slower! 100s MB/s Yet cheaper! Yet bigger! YesSequential FlashHard disksMagnetic tapes Random access like RAMLatency from rotation +Strictly sequential access but by pages like hard disksarm positioning=> un-/rewinding latency Tête Mouvement du bras Bras Pistes Secteur 10K RPM Head Tracks Sector Arm Arm movement

5. ICC Module 3 Lesson 3 – Storage 4 / 6 © 2015 Ph. Janson The need for structure in data storage Unstructured data = dumped without ordered or classification ►Easy to dump, store, transport ►But hard to retrieve, explore, exploit ►In the ocean of unstructured web data retrieving information on a statistic professor called Michael Jordan is an real challenge Structured data = stored into lists, piles, hierarchies, tables, etc. ►Easy to retrieve, explore, exploit ►Hard to maintain, store, transport ►Retrieving information on statistics professor Michael Jordan in databases of organizations that he is involved in is trivial

6. ICC Module 3 Lesson 3 – Storage 5 / 6 © 2015 Ph. Janson The need for structure in data storage ►Imagine a hard disk without any structure ►How can one know whether it is full or empty? How can one find information on it ? One might as well look for  A needle in a haystack  A song in a music library without a catalog  The works of a composer in a library classified by interpreters  The works of an unidentified interpreter about which one only know the title of one song  A song of which one only knows a few words and notes but neither the title nor the author ►Even Google needs structure to produce answers to our queries !!

7. ICC Module 3 Lesson 3 – Storage 6 / 6 © 2015 Ph. Janson Basic principle for storing structured data Catalogs / directories for storing structural relations (= “metadata”) Area for storing “data“ themselves without further logical structure