Linux server hardware and RAID configuration (detailed diagram)

1. RAID disk array

1.1 Commonly used RAID levels

• It is the abbreviation of Redundant Array of Independent Disks, Chinese abbreviated as Redundant Array of Independent Disks
• Combine multiple independent physical hard disks in different ways to form a hard disk group (logical hard disk), thereby providing higher storage performance than a single hard disk and providing data backup technology
• The different ways of composing a disk array are called RAID Levels (RAID Levels)
• Common RAID levels: RAID 0, RAID 1, RAID 5, RAID 6, RAID 1+0, etc.

1.2 RAID 0 (striped storage)

• RAID 0 continuously divides data in units of bits or bytes, and reads/writes them on multiple disks in parallel, so it has a high data transfer rate, but it has no data redundancy.
• RAID 0 simply improves performance, and does not provide a guarantee for data reliability, and one of the disk failures will affect all data
• RAID 0 cannot be used in occasions with high data security requirements

1.3 RAID 1 (mirrored storage)

• Realize data redundancy through disk data mirroring, and generate mutually backup data on a pair of independent disks
• When the original data is busy, the data can be read directly from the mirror copy, so RAID 1 can improve the read performance
• RAID 1 has the highest unit cost in the disk array. But it provides high data security and availability. When a disk fails, the system can automatically switch to the mirror disk for reading and writing, without the need to reorganize the failed data

1.4 RAID 5

• N (N≥3) disks form an array. One piece of data generates N-1 stripes, and there is also a piece of check data. A total of N pieces of data are stored cyclically and evenly on N disks.
• N disks read and write at the same time, the read performance is very high, but due to the problem of the verification mechanism, the write performance is relatively low
• (N-1)/N Disk utilization
• High reliability, allowing one disk to be damaged without affecting all data

1.5 RAID6

• N (N≥4) disks form an array, (N-2)/N disk utilization
• Compared with RAID 5, RAID 6 adds a second independent block of parity information
• Two independent parity systems use different algorithms, even if two disks fail at the same time, it will not affect the use of data
• Compared with RAID 5, there is greater "write loss", so the write performance is poor

1.6 RAID 1+0 (mirror first, then stripe)

• N (even number, N>=4). After the two disks are mirrored in pairs, they are combined into a RAID 0
• N/2 disk utilization
• N/2 disks write at the same time, N disks read at the same time
• High performance and high reliability

1.7RAID 0+1 (stripe first, then mirror image)

• The read and write performance is the same as RAID 10
• Security is lower than RAID 10

RAID level	Number of hard drives	Disk utilization	Is there a check?	Protection ability	Read and write performance
RAID0	N	N	no	no	N times of a single hard drive
RAID1	N (even number)	N/2	no	Allow a device failure	Need to write two pairs of storage devices, each as a backup
RAID5	N>=3	(N-1)/N	Have	Allow a device failure	Need to write calculation check
RAID6	N>=4	(N-2)/N	Have	Allow two device failures	Need to double write calculation verification
RAID10	N>=4 (even number)	N/2	no	Allow one of the two basis sets to be bad	Simultaneous writing of N/2 disks

2. Create a soft RAID disk array

2.1 Check the command package mdadm

rpm -q mdadm
yum install -y mdadm

2.2 fdisk tool

Use the fdisk tool to divide the new disk devices /dev/sdb, /dev/sdc, /dev/sdd, /dev/sde into primary partitions sdb1, sdc1, sdd1, sde1, and change the ID mark number of the partition type to "fd "

First create 4 new hard disks for testing.


Use the fdisk tool to divide the primary partition and change the ID of the partition type to "fd"

fdisk /dev/sdb
fdisk /dev/sdc

2.3 Create RAID Device

Create RAID5

mdadm -C -v /dev/md0 [-a yes] -l5 -n3 /dev/sd[bcd]1 -x1 /dev/sde1
 
-C：表示新建；
-v：显示创建过程中的详细信息。
/dev/md0：创建 RAID5 的名称。
-a yes：--auto，表示如果有什么设备文件没有存在的话就自动创建，可省略。
-l：指定 RAID 的级别，l5 表示创建 RAID5。
-n：指定使用几块硬盘创建 RAID，n3 表示使用 3 块硬盘创建 RAID。
/dev/sd[bcd]1：指定使用这四块磁盘分区去创建 RAID。
-x：指定使用几块硬盘做RAID的热备用盘，x1表示保留1块空闲的硬盘作备用
/dev/sde1：指定用作于备用的磁盘

2.4 Create RAID10 (mirror first, then stripe)

mdadm -Cv /dev/md0 -l1 -n2 /dev/sd[bc]1
mdadm -Cv /dev/md1 -l1 -n2 /dev/sd[de]1
mdadm -Cv /dev/md10 -l0 -n2 /dev/md0 /dev/md1

2.5 View RAID Disk Details

cat /proc/mdstat		           查看RAID磁盘详细信息和创建RAID的进度
或者
mdadm -D /dev/md0                  

watch -n 10 'cat /proc/mdstat'     用watch命令来每隔一段时间刷新/proc/mdstat 的输出

mdadm -E /dev/sd[b-e]1             检查磁盘是否已做RAID

2.6 Create and mount a file system

mkfs -t xfs /dev/md0
mkdir /myraid
mount /dev/md0 /myraid/
df -Th
cp /etc/fstab /etc/fstab.bak
vim /etc/fstab
/dev/md0      /myraid        xfs   	 defaults   0  0

Create and mount

2.7 Achieve failure recovery

mdadm /dev/md0 -f /dev/sdb1 		模拟/dev/sdb1 故障
mdadm -D /dev/md0					查看发现sde1已顶替sdb1

mdadm命令其它常用选项
-r：移除设备
-a：添加设备
-S：停止RAID
-A：启动RAID

2.8 Create the /etc/mdadm.conf configuration file to facilitate the management of software RAID configuration, such as start and stop

echo 'DEVICE /dev/sdc1 /dev/sdb1 /dev/sdd1' > /etc/mdadm.conf
mdadm --detail --scan >> /etc/mdadm.conf