dection 5Storage Devices.docx

The first of these is mirroring with mirroring you

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The first of these is mirroring. With mirroring, you set up a two drive mirrored array. It looks a lot like the striped array that we saw up above. You have two hard disk drives, and they're connected together in an array. Now just like with a striped array, the operating system sees these two drives as one logical hard disk drive in a mirrored array. For example, if we're setting up a hardware RAID array, these two disks together might be C:\ on the Windows server system.
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In a mirrored array, if we have a piece of information that needs to be written to the hard disk drive,we take this one piece of information here and we write a duplicate copy on both hard disk drives at the same time. It's not split up like with striping, it's a full copy written to both hard disk drives. Doing this does not increase the speed of the system at all like striping does, but it does increase redundancy. If something bad were to happen to this hard disk drive, and it were to go down, our data would still be okay, because an exact copy of this data is written to this hard drive as well. In fact, most RAID systems can be configured so that if one drive in a mirrored array goes down, the other drive automatically takes over for it. So if your users are working on a file when this drive goes down, they will not notice any difference.They'll keep doing what they were doing, and the work will be saved over here on this hard disk drive. Now mirroring is good, but there is still a single point of failure. When we set up mirroring, we use one RAID controller to control the mirrored drive array. This one RAID controller represents a single point of failure. If the RAID controller were to have an imperfection, a problem during manufacturing,or if it were to get shocked by ESD, or something that caused it to fail, we would lose all of our data,even though it was mirrored, both hard drives would no longer be operable. In order to get around this, we can implement duplexing. Duplexing 4:51-5:33 Duplexing looks a lot like mirroring. We still have our two hard disk drives, but instead of connecting them to a single controller, we connect one hard drive in the mirrored array to one RAID controller.Then we connect the other hard disk drive in the mirrored array to a different RAID controller. Then, when the data needs to be written, it is written to both disks at the same time, just like with mirroring.But it goes through two different RAID controller boards. The advantage to this is if this board were to go bad for some reason, our disk I/O operations would still continue. Users wouldn't notice any difference, because this RAID controller would take over and continue servicing requests using this hard disk drive until you have a chance to replace this part over here.
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