MCITP Administrator Planning for Reduction with a new drive
When RAID 5 was first introduced to the world, a lot of administrators called it ?black magic.?And that?s because they just couldn?t ?gure out how it worked! Most adminis – trators, including me, just looked at RAID 5 and knew it provided speed increases and redundancy.
But most people could never ?gure out how it really worked. The truth is, RAID 5 is actually fairly easy to explain?though I imagine it wasn?t quite as easy to engineer. RAID uses aparity bit, which, in simple language, is a 1 or 0 that is placed on a drive a certification that is dedicated to storing parity bits.
A parity bit is responsible for answering this question: Is this data different RAID 5 uses a minimum of three drives?two that store data and one that stores the parity bits. The way the parity bit comes about is by taking data on the first drive, compar- ing it with data on the second drive, and saying ?Is this different??So, for example, say you have three drives, as shown in Figure 8.1.
In row A, Drive 1 has a 1 in its first bit, and Drive 2 has a 0 in its first bit. Those two numbers are different. Thus, the parity bit is set to 1. It really just says this: ?True. These are different. On row B, Drive 1 has a 1 in its second bit, and Drive 2 also has a 1. Since these are the same, the parity bit has been set to 0 and basically says this: ?False. These are not different.?
Well, my data is gone, right? Wrong. I have a parity drive! By looking at this, I can do as you see in Figure 8.3, compare this data, and say this: ?Well, if the parity bit is a 0, I can assume this data is the same. If it’s a 1, I can place the opposite data from what’s contained in the working drive.?
So if you lose one of the drives with your data on it, the parity bit can help you 70-680 rebuild the data! But what if you lose the parity drive itself? No worries, you’ll be perfectly ?ne. That?s because this drive is used to store only parity information, not actual data like the main drives. In this case, you could replace the failed parity drive with a new drive that would rebuild its parity information by comparing the two existing drives bit by bit. RAID 5 has a huge advantage. It’s both fast and offers redundancy. But there are also some major downsides. For one thing, it’s expensive and requires at least three drives. Also, just like RAID 0, RAID 5 cannot be booted from unless you have a hardware RAID card. However, for a high-budget enterprise solution, RAID 5 is priceless.
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