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A closer look at RAID 1, also known as Mirrored Drives.

How does it work?

It requires minimum of 2 hard drives, and what happens in the RAID system is that RAID-controller will keep two identical sets of data.

Advantages:

It has increased Read speed which we’ll take a look at later in the video, and Redundancy.

Disadvantages:

Low Capacity yield.

Here we have the example. It is the same as in RAID 0 video; we have two hard drives 1TB each. We have our trusty RAID controller, and below is how operating system sees them as 1TB hard drive. This is what I meant by low capacity yield. The operating only sees as 1TB hard drive though you have two 1TB hard drives. So you only get half of the total capacity.

HDD #1 (1TB)

HDD #2 (1TB)

Virtual HDD (1TB)

RAID

When the operating system you are using is writing data to the drive, the RAID controller will simply take the data represented by this 8bits and will write them to both the hard drives. So hard drive #1 and #2 will be identical. That’s why it is called as mirrored RAID array. If you see below it just takes data and puts them on both drives, and it’s going to keep doing like that forever hopefully!

 

 

HDD #1 (1TB)

HDD #2 (1TB)

Virtual HDD (1TB)

10101010

10101010

10101010

RAID

HDD #1 (1TB)

HDD #2 (1TB)

Virtual HDD (1TB)

10101010

10101010

10101010

11001100

11001100

RAID

11001100

HDD #1 (1TB)

HDD #2 (1TB)

Virtual HDD (1TB)

10101010

10101010

10101010

11001100

11001100

RAID

11001100

10011001

10011001

10011001

HDD #1 (1TB)

HDD #2 (1TB)

Virtual HDD (1TB)

10101010

10101010

10101010

11001100

11001100

RAID

11001100

10011001

10011001

10011001

10111011

10111011

10111011

HDD #1 (1TB)

HDD #2 (1TB)

Virtual HDD (1TB)

10101010

10101010

10101010

11001100

11001100

RAID

11001100

10011001

10011001

10011001

10111011

10111011

10111011

11111111

11111111

11111111

What happens in the case of a hard drive failure?

You see here hard drive #2 just failed, and all the data on it is gone.

HDD #1 (1TB)

X

Virtual HDD (1TB)

10101010

10101010

10101010

11001100

11001100

RAID

11001100

10011001

10011001

10011001

10111011

10111011

10111011

11111111

11111111

11111111

HDD #1 (1TB)

X

Virtual HDD (1TB)

10101010

X

10101010

11001100

X

RAID

11001100

10011001

X

10011001

10111011

X

10111011

11111111

X

11111111

But because of its mirrored drive, all the data are still available in hard drive #1. So the operating system will be able to Read and Write to the disks drive and no data is gone. Hence “all your data is safe”.

And what happen when you put a new drive into the system?

Well either automatically or manually it can read through the system, and what happens is that the RAID controller will just take the data from disk # 1 and copy it to disk #2. It will do that until all the data is safely copied, and the result is, you have rebuilt your disk array and you did not lose a single file!

Summary

RAID 1 requires at least 2 hard drives to implement. In RAID 1 two 1TB hard drives is seen by RAID controller as one 1TB hard drive since the other hard drive is used for duplicating the data present in one drive which is called as mirroring.  So both the hard drives contain the same data. The read speed is faster than a single drive. RAID 1 array provides redundancy by duplicating all the data from one drive on a second drive so that if either drive fails, no data is lost.

The downside of RAID 1 array is its low capacity yield since the hard drives are not seen as cumulative unit. Hence the cost per bit of disk storage is twice that of a single drive as two drives are needed to store the data. The write speed is slower than RAID 0 since all writes need to be duplicated to both disks in the mirror.

Conclusion

RAID 1 storage array offers redundancy due to mirroring. If one drive fails, the data is still safe on the second drive and can be rebuilt to a new hard drive from there.