What is Raid anyway

Back in the 1980th the acronmy RAID was coined in University of California, Berkeley in 1987 and stands for "Redundant Arrays of Inexpensive Disk". Inexpensive at the time was a couple of 1000 $ for a disk storing a few Megabyte. And Redundant means that that the data on the disk was somehow duplicated on other disk so the service could continue even when a disk failed.
Large server manaufactors have engineered this and other features in the mid 1990th into there hardware to archive scalability and availbiltty. The most advanced was Digitals Tru64 Unix that resemebeld modern cloud features already in the mid 1990th.

Raid levels

What geeks at home want it but small busineean and large enterprise require are two caracteritics: uninterrupted availability of the service and good performance.
Diffrence in the RAID LEVELS is how this charaterisitcs are distributed and how much capacity you have to sacrisfy. Yes to have availablility you actualy need to scarace disk which are not a avialble for storage storage.
From the standard the only the Raid level 0,1 5,6 and Raid 1+0 a popular combination of mirroing and striping.

RAID 0 - Striping For Performance

With a RAID 0 all the disks in a RAID-Set are stripped, that is accessed in parallel. This gives you up to n time the performance fro reading and writing but it does not provide any redundency in case a drives fails. IT also does no cost you any capacity.


RAID 5 and 6

= JBOD Just a bunch od Disk

Status: Draft Date: 2014-10-15 00:23:19 +0200 (Wed, 15 Oct 2014) Revision: 27

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