LM3 – Storage

First, as we move forward, please keep Kryder’s Law in mind.

This menu and sub-menu area contains:

1. Lecture Recording of the text material as presented in class (i.e. textbook material + additional content) embedded below

2. RAID presentation (still under-construction) in the submenu. You are responsible for the concepts of striping, mirroring and MTTF but not the individual RAID levels beyond RAID levels 1 & 2.

3. Forensics Lecture Recording located in the OS submenu.

Lecture Recording but please continue to read the material on this page

Memory/Storage Hierarchy

The Memory or Storage Hierarchy is located here if you need a refresher:  http://en.wikipedia.org/wiki/Memory_hierarchy.

Magnetic Disks

First please read the following on HDD: http://en.wikipedia.org/wiki/Hard_disk_drive

With respect to magnetic disks please understand or recall that instructions and data must be in memory to be processed and the HDD suffers from mechanical (access) and transfer latencies which render it orders of magnitude slower than memory and the CPU.

The smallest addressable unit is the sector however sectors are more often grouped into clusters in powers of 2. Clusters are typically at least 2048 bytes although smaller USB drives can be formatted with smaller clusters (please see the link below for a description of tracks, sectors and clusters).  This means that if the computer needs to read in or modify a single Byte on the disk, the computer must transfer the entire sector/cluster.


Now putting this all together and recalling the memory/storage hierarchy and its categorization, we understand why having data and programs in memory speeds execution and why increasing memory size often results in significant performance improvements.



Solid State Drives (SSD)

SSDs are both the present and the future.  It is important to note that flash memory can be based on NAND or NOR technology (NAND & NOR logic coming in Programming Languages).  NAND is block accessible similar to HDs and is the basis of SSD storage devices (Fast erase, write and very good read performance).  NOR is byte addressable (in accord with RAM) and is rapidly replacing EEPROM (fast read performance but slower write performance).  Please see here:  http://en.wikipedia.org/wiki/Ssd

A recent emergence are hybrid drives (what Apple calls “the fusion drive”) which blend magnetic and SSD drives to obtain fiscally reasonable performance improvements.  Apple’s Fusion Drive is different than the text’s presentation of an integral Hybrid Drive (Magnetic HD with SSD Cache) as the Fusion Drive has separate HD and SSD and OSX manages their complimentary functionality.  OSX will track user computing behavior and migrate often used apps to the SSD for quicker access.

Wikipedia Hybrid Drives: http://en.wikipedia.org/wiki/Fusion_Drive

Apple Fusion Drive: http://www.zdnet.com/apples-fusion-drive-hybrid-done-right-7000006248/

Error Detection – see parity bit document below.

Cloud Storage

Cloud Storage presents many cost effective opportunities and concommittant risks (see 2014 Apple iCloud celebrity data breach among other concerns). We know about free public cloud storage offered by box.net, dropbox and Google (i.e. Gdrive). In class I presented that 2 separate Chinese companies are offering 1 TB and 10 TB of free storage respectfully (search storage tag in right panel).  If companies are offering free storage – What is their business model and what do they get out of it? Of course the answer is in the lecture recordings above.

Future of Storage

Now above I stated that SSDs are our immediate future but we accept that we are living through emergent and disruptive change so consider that IBM has shattered Kryder’s law storing 1 bit on 12 atoms and Harvard has recently stored 70 billion books using DNA.  Harvard scientists predict that “The total world’s information, which is 1.8 zettabytes, [could be stored] in about four grams of DNA,”.  You can read more as these developments in the Emergent Topics Blog with tag – Storage.

Now consider Big Data where the typical data set is over 1 TB.  Also consider that data must be in memory to be processed.


Additional Topics/Resources

If nothing else please become familiar with backup strategies as data/information resiliency, availability and regulatory compliance is paramount in today’s environment.  http://en.wikipedia.org/wiki/Back_up

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