This post is the second part of the Wonderful RAID Family – part 1
Host: “Hello everyone, welcome back to the container rebuild show part 2. Let’s make some noise to welcome the upcoming RAID family member, RAID-1, RAID-5 and RAID-10!!!”
RAID Family- RAID 1
RAID-1 stepped on to the stage and said: “I am good at turning things into mirroring function. Today, let me separate AB and CD to two relatively identical containers, then pour water into A and C containers. Moreover, here comes the magic part! You can see B and D containers also have the same liquid capacity just like A and C! This is what mirroring can do!
RAID-1 “Oops! I accidentally break the A and C container! How bad it is!
Then, RAID-1 put a blanket on the containers and said: “Here comes the magic part! Three! Two! One! (Take the blanket out) Ding dong! A and C containers are coming back because of B and D containers!”
(Suddenly, a child kicked a ball to the stage and broke the A and B container)
RAID-1: “Ohh!!!NO!!! The pairs of container are broken. Now there’s nothing we can do to turn it back…..
RAID-1 has disk mirroring backup mechanism, to start the process, it requires even number of the hard drive for the first condition. When hard drive completed RAID-1 combination, the sufficient storage capacity is only half of the total drive capacity because all data get written twice. After that, the disks will mirror images of each other, so if one disk fails, the other one can retrieve the data. This mechanism allows fault-tolerant with half of the hard drive can be failed each time. However, when the damaged hard drives are two hard drives that are mirroring each other, then the files cannot be retrieved.
Host: “OK! Let’s welcome the next member RAID-5!!”
RAID-5: “Hello everyone, I am good at pouring everything into two or more containers at the same time. For example, there are four containers on the table, and I can split liquid into three and pour them into three containers. For the remaining one, I will put a unique tracking item that will help me track the liquid I have poured in each time. Just like right now, I can pour the first liquid into A, B, C containers at the same time then put the tracker into D containers to record the first one. Then pour the second liquid into B, C, D containers and put the second tracker into A container…and so on. So when I have all the liquid filled, there will be an entire container capacity is used to place trackers.
RAID-5 finished pouring liquids and said: “The feature of the container I have made is that when there’s a hole in one container and the part of liquid is leaking, I can replace that broken container and use the tracker to track back the liquid I have poured in! But please note! If there two containers were broken, then that will be a big trouble! Because in that case, the tracker will be gone and I can use it to find the losing liquid! So I cannot longer repair broken containers.
RAID-5 is the most used RAID settings, faster than RAID-0, but also has a RAID-1 mirroring disk mechanism.
The RAID-5 operation mode is to divide written files into at least two parts of data and add a parity check code at the same time. Also, these three copies (or above) of data will be cyclically written to different hard disks in sequence, so it means that RAID-5 need at least three hard drives to form the condition. Which says the cost is relatively high and the total capacity will need to subtract one drive due to the check code.
In RAID-5 status, when there’s one hard disk failed, the other hard drives can still be working without effect. Just replace the failed hard drive, then the data will be rebuilt back to the original status.
However, please note that RAID-5 only allows one hard disk failure each time, if there are more than two hard disks fail to work, then the data cannot be restored anymore.
Host: “Thank you so much for everything seeing RAID family’s magic show. Our show is going to end and let’s welcome our final guest! RAID-10!”
RAID-10: “Thank you so much for coming to this show! I am RAID-10, my magic is to combine my RAID family member RAID-1 and RAID-0’s magic into my power! See! I can turn A、B、C、D containers into two pairs and mirroring, just like what RAID-1 can do.”
RAID-10: “ Then, just like RAID-0, I will connect two mirroring pairs AB and CD into a big container! Then I will pour the liquid into these two mirroring containers at the same time. So, if one container did not work or be broken, I only need to replace the new container, and everything including data will be still working fine.
(RAID-10 take a bottle of liquid and display his magic, just like RAID-0, he can pour the liquid into A and C at the same time. Suddenly, magic happened again! Just like RAID-1, RAID-10 make B mirroring A and D mirroring C, to let them have the same liquid in B and D containers! )
RAID-10: My container’s feature is when if there anything happened to A, C or B, D containers, you can replace the failure container and everything will work just fine. However, if I break the containers that mirroring to each other, then I will just like my family member RAID-1, and will not able to restore the liquid back, and the containers will not be using after that.”
What RAID-10 can do is to divide A, B, C, D four hard disks into two groups, each group do the mirroring backup first, then string two groups together into a large-capacity hard disk. To speak easily, RAID-10 is a mechanism that does the RAID-1 first then does the RAID-0. So the total capacity will be only half of all hard disk capacity. Moreover, the fault tolerance allows up to simultaneous failure of two hard disks, but the premise is that two damage disk cannot be the combination of mirroring backup hard disk.
Host: “Thank you so much for you coming today! Our container rebuild show has finally come to an end! We will launch more RAID family magic show for everybody in the future.
And our boss – ITE2 NAS just said there would surely be more exciting performances in the future! Please stay tuned to our news and thank you so much again!!”