RAID

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hi all, i am having problems understanding RAID, could some one explain exactly what redundant and non redundant drives are,also if using RAID 0 (striping) as both drives are attatched to the same controller and both assigned the same letter, how are you supposed to determine the faulty drive if one occurs? thanks robbo1962

 

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Hi Robbo,

What material are you using for your studies? I would recommend All in One A+ by Mike Myers if you haven't already bought a book. As for RAID, take a look here

 

Yo, Robbo.

Hard drives. Gotta have one, but more are better!

So, let's put another in there. All of a sudden we've got not only extra storage, but in the case of a server the possibilities for speeding things up and/or securing data are also viable.

RAID: Redundant Array of Inexpensive (old term) Independent (new term) Disks (or devices).

Ok, so the redundancy is in you can lose one (or more) disks and still retain your data. Hm.

Raid 0 = Disk striping. The data is saved to two (or more) HDDs, one half of the data (say a word doc) is saved to one HDD and the other half to the other - zip,zap,zip,zap. Speeds things up no end, retrieval's quick too. But what if one goes a bollock? All your data is lost. (Just a quick point here - as a tech it's never your data, it's always someone elses - data is king)

Raid 1 = Disk mirroring (or duplexing and I can't be arsed at this time of night). The idea here is that you save the same data to two HDDS. Takes a while to save cos your system is saving the same stuff to two drives - zip...zip...(yawn) zap...zap...(yawn) But of course you've now got two copies of your (their) data so if one HDD dedcides to get the clatters then the data is safe.

Raid 2,3,4 = If you want any more than the A+ wants from you as a student then research it yourself.

Raid5 = Disk striping with parity. You're going to need three HDDs for this one. The idea here is that (little bit of maths) if you can say that 2x3=6 then if you were to take away one of the parts you could make it up from the bits that were left. ie 2x?=6, ?x3=6, 2x3=? The point is that it's striping (so quicker) mirroring (sort of) and safe (cos if you get one HDD go down you can stick in another and the other two can 'make up' the missing bits and put them back on the third).

How much fun was that?

All the best,

J.

 

thanks for the replies but my main problem is understanding what redundancy and non redundancy drives actually mean

 

Redundancy

 

Redundancy = Fault tollerant = One of your drives dies, others still function.

With RAID 1 (Mirroring) if one of your drives dies the other still keeps the system going, as it was an exact copy of the drive that died. You of course loose your fault tollerance / redundancy until you replace the failed drive and re establish the mirror.

With RAID 5 (Striping with Parity) you must have at least three disks. You loose the storage capacity of one of the disks as this is used for the parity. When one of the drives dies the other two will continue to work. when you re-add the third disk the "parity" from the other two disks restores the data that was on the original disk.

Hope this helps!

 

i usually go by the bright, flashing red light on the disk itself. it does tend to stand out in a sea of green lights.
and the high priority notification mails sent by the monitoring tools are also a dead giveaway.

 

from your link to the definition Boyce, would i be right in saying a redundant disk drive just mirrors another one but a non redundant drive will be part of a set of drives each having different data stored on it as in striping? I am using the all in one Mike Meyers A+ to study but your definition seems clearer to me.

 

Blimey if I'd thought it was simple semantics I could have saved meself some time!

Overclocked the thought processes again.

Ah well, it shows that some of it vaguely sunk in!

J.

 

I was a bit confused about RAID also, untill I found this website...

http://www.acnc.com/04_01_00.html

Really helped me understand what it's all about.

 

Great link, thanks