dection 5Storage Devices.docx

Parity 534 626 the next raid concept that you need to

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Parity 5:34-6:26 The next RAID concept that you need to understand before we move on is parity. Mirroring and duplexing work very nicely, but we don't get the speed advantage introduced by striping. Parity allows us to use striping with some degree of redundancy or fault tolerance. When we set up parity, we set up a striped array. In this example, let's say we set up a striped arraybetween these two disks right here, and then we add a third disk to the array that contains parity information. This parity information can be used to reconstruct data if something bad happens to one of the disks in the striped array. Also, depending on the rate level, we can use either the entire disks or part of the three disks. Now we have created a striped array that has some redundancy to it. In other words, if this disk were to go down, we can reconstruct the missing data from the parody information over here. Implementing RAID 6:27-7:40 Now let's talk about how we implement RAID itself. There are two different ways you can do it. Most of the time when you're implementing RAID, you're going to purchase a RAID controller card,and install it into your system. Many servers come with a RAID controller built into the system, and you don't actually have to install a card. Others you will have to go out and purchase a card and install it. However, that's not the only way to do it. You can also implement RAID using software. Most network operating systems support software RAID. In other words, instead of using a hardware card to manage the RAID array, we use the CPU and the operating system to create the RAID array. The software RAID works very well. It's easy to implement, and it's less expensive because you don't have to go out and purchase a new RAID card. However, it is slightly slower than using the hardwareRAID. With hardware RAID, we have a chip on the RAID card that is dedicated to doing nothing otherthan managing that RAID array. If we implement software RAID, then we have to use part of our CPU time to perform RAID operations. Instead of using the chip on the RAID card. Either way works, but given the choice, I would always go with hardware RAID over software RAID. With that in mind, let's talk about RAID levels. RAID 0 7:41-8:13 Let's start with RAID zero. RAID zero is just simple plain old striping. We talked about striping before,and we used this diagram. Well, RAID zero is just that, it's striping data between two hard disk drives. While RAID zero can dramatically increase your throughput to and from the hard disk drive, it does not provide any redundancy. If this drive over here were to die, you've lost all the data on your system because your files are split between the two hard disks. RAID 1 8:14-8:59 We also have a RAID level called RAID 1. Now before we go any further, we do need to point out that the lower the number, does not mean that it is a worse or a less desirable RAID level, or that the higher the number, the better the RAID level is. The RAID number is used to distinguish how a RAID array is configured, or how the hard drives are implemented into the array.
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  • Spring '14
  • Serial ATA

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