Introduction to Linux-RAID Disk Array
1. Detailed explanation of RAID disk array
1. Meaning
- RAID disk array is the abbreviation of Redundant Array of Independent Disks, Chinese abbreviated as Redundant Array of Independent Disks. Multiple independent physical hard disks are combined in different ways to form a hard disk group (logical hard disk), thus providing higher than a single hard disk. Storage performance and the different ways of providing data backup technology to form a disk array are called RAID Levels (RAID Levels)
2. Commonly used RAID levels
RAID 0 ， RAID 1 ， RAID 5 ， RAID 6 ， RAID1 0
3、RAID 0
- 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 is just pure Improved performance 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.
4、RAID 1
- RAID 1 (mirror storage)
RAID 1 realizes data redundancy through disk data mirroring, and generates mutually backup data on a pair of independent disks.
When the original data is busy, the data can be directly read from the mirror copy, so it can Improve read performance
RAID 1 is the highest unit cost in the disk array, but 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
5、RAID 5
- RAID 5
RAID 5 is composed of N (N>=3) disks. One piece of data produces N-1 stripes, and there is also one piece of parity data. A total of N pieces of data are stored in a circular and balanced manner on N disks.
RAID 5 N disks read and write at the same time, and the read performance is very high, but due to the problem of the check mechanism, the write performance is relatively low.
RAID 5 disk utilization rate is (N-1)/N
RAID 5 has high reliability and allows failure 1 disk, does not affect all data
6、RAID 6
- RAID 6
RAID 6 is composed of N (N>=4) disks, and (N-2)/N disk utilization.
Compared with RAID 5, RAID 6 adds a second independent parity information block
RAID 6 two An independent parity system uses different algorithms, even if two disks fail at the same time, it will not affect the use of data.
Compared with RAID 5, RAID 6 has a greater "write loss", so the write performance is poor.
7、RAID 1+0
- RAID 1+0 (mirror first, then stripe)
N (even number, N>=4) After two disks are mirrored, they are combined into a RAID 0
N/2 disk utilization rate
N/2 disks are written at the same time , N disks can be read simultaneously
with high performance and reliability
8、RAID 0+1
- RAID 0+1 (stripe first, then mirror)
read and write performance is the same as RAID 10,
security is lower than RAID 10
| AID level | Number of hard drives | Disk utilization | Is there a check? | Protection ability | Write performance |
|---|---|---|---|---|---|
| AID0 | N | N | no | no | N times of a single break |
| AID1 | N (even number) | N /2 | no | Allow a device failure | Need to write two pairs of storage devices, each as a backup |
| AID5 | N>-3 | (N-1)/N | Have | Allow a device failure | Need to write calculation check |
| AID6 | N>-4 | (N-2)/ N | Have | Allow two device failures | Need to double write calculation verification |
| Aid10 | N>-4 (even number) | N /2 | no | Allow one of the two basis sets to be bad | Simultaneous writing of N/2 disks |
2. Array card introduction and real machine configuration
1. Overview of the array card
- Array card
- Array card is a board used to realize RAID function
- Usually composed of a series of components such as I/O processor, hard disk controller, hard disk connector and cache
- Different RAID cards support different RAID functions,
such as RAIDO, RAID1, RAID5, RAID10, etc. - RAID card interface type
IDE interface, SCSI interface, SATA interface and SAS interface
2. Cache of the array card
Cache of the array card Cache is the place where the RAID card exchanges data with the external bus. The RAID card first transfers the data to the cache, and then exchanges data between the cache and the external data bus
. The size and speed of the cache are directly related to the reality of the RAID card. Important factors for transmission speed
Different RAID cards are equipped with different memory capacities when they leave the factory, generally ranging from several megabytes to hundreds of megabytes.
3. Example: Building a soft RAID5 disk array
- Steps to create a soft RAID5 disk array:
- Create 4 10G hard disks in the virtual machine and boot
- Check whether the mdadm package has been installed
rpm -q mdadm
yum install -y mdadm
- View the partition situation and create a partition (ID tag number is "fd")
fdisk -l-view the partition
fdisk /dev/sd[be] -create a partition (the picture is an example of sdb partition)
- Create a RAID5 device
mdadm -Cv /dev/md5 -l5 -n3 /dev/sd[bcd]1 -x1 /dev/sde1
-C: means to create a new:
-v: display detailed information during the creation process.
/dev/md5: Create the name of RAID5.
-a yes: --auto, which means that if any device file does not exist, it will be created automatically, which can be omitted.
-l: Specify the level of RAID, l5 means to create RAID5.
-n: Specifies to use several hard disks to create RAID, n3 means to use 3 hard disks to create RAID.
/dev/sd [bcd]1: Specify these 3 disk partitions to create RAID.
-x: Specify several hard disks to be used as hot spare disks for RAID,
x1 means to reserve 1 free hard disk as a spare /dev/sde1: Specify the disk to be used as a spare
View the detailed information of RAID disks
cat /proc/mdstat (also View progress)
or mdadm -D /dev/md5
use the watch command to refresh the output of /proc/mdstat at regular intervals
watch -n 5 "cat /proc/ mdstat' to
check whether the disk has been RAID
mdadm -E /dev/sd [be]1
- Create and mount the file system
mkfs -t xfs /dev/md5 (mkfs.xfs /dev/md5)
-format mkdir /md5-create directory
mount /dev/md5 /md5-manually mount
df -Th- - View
automatically mount (Linux disk management and file system introduced here but to explain)
cp / etc / fstab /etc/fstab.bak
vim / etc / fstab
/ dev / MD5 - / MD5 - XFS - defaultsI ——0——0 - Simulate fault
mdadm /dev/md5 -f /dev/sdb1——simulate /dev/sdb1 fault
mdadm -D /dev/md5——check that sde1 has replaced sdb1, and sdb1 is in faulty state
- Achieve failure recovery (method one)
mdadm /dev/md5 -r /dev/sdb1——remove
mdadm /dev/md5 -a /dev/sdb1——add
at this time sdb1 is the backup spare state, indicating that the failure recovery
can achieve failure recovery (Method 2)
Create the /etc/mdadm.conf configuration file to facilitate the management of software RAID configuration, such as starting and stopping
echo'DEVICE /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1'> /etc/mdadm .conf
mdadm --detail --scan >> /etc/mdadm.conf
cat /etc/mdadm.conf
umount /dev/md5
mdadm -S /dev/md5
mdadm -As /dev/md5
- Summary of other commonly used options of mdadm command
-r: remove device
-a: add device
-S: stop
-A: start
mdadm dev/md5 -f /dev/sdb1 (simulated failure)
mdadm dev/md5 -r /dev/sdb1( Remove)
mdadm dev/md5 -a /dev/sdb1 (add)
echo'DEVICE /dev/sdc1 /dev/sdb1 /dev/sdd1'> /etc/mdadm.conf
mdadm --detail --scan >> /etc /mdadm.conf
umount /dev /md5
mdadm -S /dev/md5
mdadm -As /dev/md5
-s: refers to finding the configuration information in the /etc/mdadm.conf file.
4. Example: constructing a soft RAID 10 disk array
Steps of creating a soft RAID1 0 disk array: (first mirroring, then striping)
- The first 3 steps are the same as RAID5, so I won’t describe them here.
- 4. Create a RAID1 0 device
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
- 5-7 is similar to RARD5, here is the text
- Format, create a directory and mount
- Simulated failure
- Achieve failure recovery