Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the required level of and performance. The different schemes, or data distribution layouts, are named by the word “RAID” followed by a number, for example, RAID 0 or RAID 1. Each scheme, or RAID level, provides a different balance among the key goals: reliability, availability, performance, and capacity. RAID levels greater than RAID 0 provide protection against unrecoverable sector read errors, as well as against failures of whole physical drives.——[RAID.wikipedia]

The test environment

• CentOS 8.0 virtual machine
• Add two hard disks
• The installation for mdadm

raid-1 operating steps

• Use LSBLK to view the current hard disk partition

lsblk

You can see that sdb and sdc are not in use

• partition for sdb and sdc

Because RAID requires the same size of each hard disk, sdb and sdc are partitioned respectively, and each hard disk is partitioned into a 16G partition, and Hex code is modified as fd

fdisk /dev/sdc

Other hard disk partition process omitted, partition after as follows:

• installation mdadm

yum install madadm

• Create a RAID-1

sdb1, sdc1 form a group of raid-1, RAID device named /dev/md0

mdadm -C /dev/md0 -a yes -l 1 -n 2 /dev/sd{c1,b1}

Check the progress:

cat /proc.mdstat 

View RAID information:

mdadm -D /dev/md0

Here we create a RAID1 disk array from mdadm

• Create the md0 profile

echo DEVICE /dev/sd{b,c}1 >> /etc/mdadm.conf
mdadm -Evs >> /etc/mdadm.con 

• Format & create directory and mount

mkfs.xfs /dev/md0
mkdir    /raid1
mount    /dev/md0 /raid1
df       -h

At this time we can go to /raid1 directory to store our files

• Write the partition table and mount automatically at startup

echo "/dev/md0 /raid1 xfs defaults 0 0" >> /etc/fstab 

Conclusion

Save A file to display of RAID 1, RAID will cut into A1, A2, A3, branch of two pieces of written to disk, can make the disk write speed slightly down, because this way is written to disk, one of the hard disk is broken, another have the same backup hard disk, so the RAID 1 is redundant support, but the cost is quite high, also only 1/2 of the disk space can be used

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