13. File System-combining raid, hardware raid, and soft RAID of different levels

From RAID 0 to raid 6, different levels of RAID compromise in terms of performance, redundancy, and price. The purpose of combining different levels of raid is to foster strengths and circumvent weaknesses and generate a hybrid raid level with advantageous features. Commonly used raid combinations include raid10, raid01, raid50, and raid05.

Raid10 is to do 1 first and then 0; raid01 is to do 0 first, and 1, raid50 and raid05 are the same.

 

I. raid10And raid01

Raid10 combines raid1 with raid0, first mirroring, and then striping. For example, there are now six hard disks, each of which forms a group of images-Raid 1, and then combine the three sets of images into RAID 0. The disk usage of raid10 is 50%, which allows bad parts in the same group of image arrays. However, if two parts in a group of image arrays are broken, the entire image is broken, the entire array cannot work.

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Raid10 features

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Raid01 divides six disks into two copies to form an image. The three disks in each copy are used as RAID 0. It allows a group of images to break down, but not both. The risk of raid01 is greater than that of RAID 10, because the possibility that each array may have a bad disk is greater than that of multiple disks in a disk image. Therefore, raid10 is more widely used for security and ease of use.

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II,Raid50And raid05

Raid50 is a combination of RAID5 and raid0. It first implements RAID5 and then strip. It is very similar to raid10. Suppose There are also six disks, each of which is made into RAID 5. There are two groups in total, which are combined into RAID 0.

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Raid50Features

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The raid50 utilization rate depends on the number of disks. For example, you can use 12 disks as raid 50. The available solutions include 3*4, 4*3, and 6*2, one of the Disks Made into RAID 5 is redundant, so three different redundancy quantities may be generated, which leads to the total number of redundancy which may be and 2, as a result, the final utilization rate may be 67%, 75%, and 83%.

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III,Commonly used raidLevel comparison

Commonly used RAID levels include raid0, raid1, raid3, RAID5, and raid10. The following table lists the differences between them:

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RaidThere are no upper or lower levels. They only have dedicated feature differences..

 

 

4. Hardware raidSoft RaidOverview

1.Hardware raid

Hardware raid has a dedicated raid control processor and I/O processing chip to process raid tasks without occupying host CPU resources. Some raid devices also have dedicated batteries for power supply to prevent data loss caused by sudden power outages. Hardware raid is expensive because of these additional devices.

The hardware raid components are completed in Bois. After the operating system is installed, raid is installed. The computer regards a group of RAID devices as a whole instead of several hard disks separately. Generally, the operating system recognizes it as/dev/SDB or/dev/SDC, it is not recognized as/dev/SDA because/dev/SDA is often reserved as an operating system device, while raid is used to store data.

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2.Software raid

The hardware raid structure is introduced above. If the RAID device does not have a raid chip, the operating system will not see a whole, but multiple independent disks. However, we still want to regard it as a whole, which requires simulation of RAID hardware functions through software. Therefore, a module is provided in the Linux kernelMultiple hardware devices are combined into one logical device.The device is called the multi devices module.

For example, the hardware on an operating system has the following three devices:

/Dev/sdb1/dev/sdc1/dev/sdd1

Now we use the MD module to simulate these three devices into a RAID (soft RAID), so we have formed such a device:

/Dev/md0/dev/md1/dev/md2 ......

The number of groups of RAID arrays is the number of/dev/MD # devices. Here, 0, 1, 2... is neither 1 in/dev/sdb1 nor raidLevelIt only represents the raid simulated by the software.Device.

The MD module must be configured with some parameters to work properly. MD is a module provided by the kernel, so these configurations also need to be completed for the kernel. The interface for interacting with the kernel is/proc, therefore, to configure MD, you must modify the parameters in the/proc and/sys files. However, it is very difficult to modify these parameters. Fortunately, there are system calls specifically for MD settings in Linux. People have developed a dedicated raid management tool through these system calls --Mdadm(Multi device administrator ). With mdadm, you can define multiple disk devices, assemble them into a RAID device, and specify parameters such as the raid level, number of disks, redundant disks, and backup disks. However, it should be noted that what actually works is MD, rather than the mdadm command.

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