Main Area and Open Discussion > General Software Discussion

RAID explained ?!

(1/3) > >>

tomos:
RAID storage explained

by George Ou at TechRepublic. Link

RAID was originally defined as Redundant Array of Inexpensive Drives, but RAID setups were traditionally very expensive so the definition of “I” became Independent.  The costs have recently come down significantly because of commoditization and RAID features are now embedded on to most higher-end motherboards.  Storage RAIDs were primarily designed to improve fault tolerance, offer better performance, and easier storage management because it presents multiple hard drives as a single storage volume which simplifies storage management.  Before we start talking about the different RAID types, I’m going to define some basic concepts first.-
-
I've been trying to get my head around RAID for a while now
I think this is a good article - in spite of the fact my eyes start glazing over after the first half page -
that has more to do with my capacity for technological info than anything else ...

tomos:
RAID Level 6:
RAID Level 6 is a cluster-level implementation of data striping with DUAL distributed parity for enhanced fault tolerance.  It’s very similar to RAID Level 5 but it uses the equivalent capacity of two hard drives to store parity.  RAID Level 6 is used in high-end RAID systems but it’s slowly becoming more common as technology becomes more commoditized.  Dual parity allows ANY two hard drives in the array to fail without data loss which is unique in all the basic RAID types.  If a drive fails in a RAID Level 5 array, you better hope there is a hot spare that will quickly restore the array to a healthy state in a few hours and you don’t get a second failure during that recovery time.  RAID Level 6 allows that second drive failure during recovery and is considered the ultimate RAID Level for fault tolerance.  Out of an array with “N” number of drives, the total capacity is equal to the sum of “N-2″ hard drives.  For example, an array with 8 equal sized hard drives will have the combined capacity of 6 hard drives.Sounds good

Hirudin:
I love that there is also "JABOD" (or is it "JBOD"?)! Just a Bunch of Drives! Haven't used it, but I guess it's like RAID except that it doesn't require the same capacity drives.

f0dder:
Hirudin: yup, it just gives you "one big disk", linearly used, without the speed advantages of striping, and slightly less chance of losing all your data (although you will need a decent filesystem recovery app if a single disk dies).

RAID-6 is imho a good idea, since disks purchased at the same time tend to die around the same time. Especially if the problem is wear&tear + heat in a crowded server room, disk #2 might die from the added stress when the system tries to reconstruct the array with help of a spare drive. And then you're screwed.

lanux128:
tomos, add this article to your list: http://en.wikipedia.org/wiki/RAID :)

Navigation

[0] Message Index

[#] Next page