Whats RAID?

[HiroProtagonist]

whats does a RAID controller do anyway?

 

[Gunbuster]

Use the forum search function and find out.

Or try something crazy like a internet search at yahoo, aksgeevs, google..............

 

[John]

RAID controls roaches...

 

[nEoTeChMaN]

Come on, let help one of our fellow members. 😉

Here is your answer....

 

[John]

The controller allows you to hook up the HDD's so you can then set up a RAID array.

 

[AMB]

RAID = Redundant Arrays of Inexpensive Disks, if you can make much sense of that, you should understand the rest:



<< <storage, architecture> (RAID. Originally &quot;Redundant Arrays of Inexpensive Disks&quot😉 A project at the computer science department of the University of California at Berkeley, under the direction of Professor Katz, in conjunction with Professor John Ousterhout and Professor David Patterson. >>





<< The project is reaching its culmination with the implementation of a prototype disk array file server with a capacity of 40 GBytes and a sustained bandwidth of 80 MBytes/second. The server is being interfaced to a 1 Gb/s local area network. A new initiative, which is part of the Sequoia 2000 Project, seeks to construct a geographically distributed storage system spanning disk arrays and automated libraries of optical disks and tapes. The project will extend the interleaved storage techniques so successfully applied to disks to tertiary storage devices. A key element of the research will be to develop techniques for managing latency in the I/O and network paths. >>





<< The original (&quot;..Inexpensive..&quot😉 term referred to the 3.5 and 5.25 inch disks used for the first RAID system but no longer applies. >>



The following standard RAID specifications exist:

RAID 0 Non-redundant striped array
RAID 1 Mirrored arrays
RAID 2 Parallel array with ECC
RAID 3 Parallel array with parity
RAID 4 Striped array with parity
RAID 5 Striped array with rotating parity

 

[Viper GTS]

RAID (Redundant Array of Independent Disks) basically turns two or more hard drives into one drive array (viewed as one large hard drive). There are several ways of achieving this:

RAID 0: Striping

Data is striped across both disks. For example, if you were using a 1-bit stripe across two disks (not that you ever would, but just for illustration), writing the byte: 10011011 would result in:

Disk 1: 1
Disk 2: 0
Disk 1: 0
Disk 2: 1
Disk 1: 1
Disk 2: 0
Disk 1: 1
Disk 2: 1

The advantage of this is that you've effectively doubled your sequential read/write speeds, since you have two disks operating in unison. The disadvantage is that if you lose one disk, your whole array is toast. And having two drives doubles your chances of losing one drive. RAID 0 is fast, but dangerous.

RAID 1: Mirroring

Data is mirrored to two disks. Both disks receive exactly the same data. Writing our same 10011011 would result in:

Disk 1: 1
Disk 2: 1
Disk 1: 0
Disk 2: 0
Disk 1: 0
Disk 2: 0
Disk 1: 1
Disk 2: 1
Disk 1: 1
Disk 2: 1
Disk 1: 0
Disk 2: 0
Disk 1: 1
Disk 2: 1
Disk 1: 1
Disk 2: 1

The advantage of RAID 1 is that you've just exponentially decreased your odds of losing your data. If you lose one drive, you have another that's identical. The chances of losing both drives at once are astronomically high, so reliability is the stronpoint of RAID 1.

RAID 0+1: Striping + Mirroring

Raid O+1 requires four disks, &amp; combines the strongpoints of RAID 0 &amp; 1. Writing 10011011 again would result in:

Disk 1/3: 1
Disk 2/4: 1
Disk 1/3: 0
Disk 2/4: 0
Disk 1/3: 0
Disk 2/4: 0
Disk 1/3: 1
Disk 2/4: 1
Disk 1/3: 1
Disk 2/4: 1
Disk 1/3: 0
Disk 2/4: 0
Disk 1/3: 1
Disk 2/4: 1
Disk 1/3: 1
Disk 2/4: 1

You have the same data striped across two pairs of mirrored drives. You get the speed of RAID 0, since you're striping across more than one drive, &amp; you also get the reliability of RAID 1, since you're mirroring each drive as you go.

Spanning

Spanning is another form of RAID that's less commonly used, because it's only real advantage is converting smaller volumes into one larger volume. Let's say you have three hard drives: a 10 gig, a 20 gig, &amp; a 40 gig. You start with the 40, &amp; when you fill it completely your data automatically flows to the 20, &amp; to the 10 when that becomes full. With large hard drives becoming commonplace, spanning is pointless, but still an option.

So what does a RAID controller do?

A RAID controller makes all these operations invisible to the operating system. The OS doesn't need to know that it's data is being written twice, four times, or even across multiple disks. The OS only sees one drive, &amp; a controller.

[EDIT]Damn, I knew I shouldn't have wasted my time. Even on a Sunday morning you guys are still too fast for me. :|[/EDIT]

Viper GTS