1、 Introduction to common RAID
The full name of disk array is (redundant arrays of inexpensive disk, RAID), which means independent redundant disk array in Chinese. Raid can integrate multiple smaller disks into a larger disk device through technology (software or hardware), and this larger disk function can not only store, but also have the function of data protection. Due to different levels selected by the whole raid, the integrated disk has different functions. The basic commonly used levels are as follows
RAID 0 (striped storage) – best performance
- RAID 0 continuously divides data in bits or bytes and reads / writes to multiple disks in parallel, so it has a high data transmission rate, but it has no data redundancy;
- RAID 0 only improves performance, does not guarantee the reliability of data, and the failure of one disk will affect all data;
- RAID 0 cannot be used in situations requiring high data security.
RAID 1 (mirrored storage) – full backup
- Realize data redundancy through disk data mirroring, and generate mutually backed up data on paired independent disks;
- When the original data is busy, the data can be read directly from the mirror copy, so RAID 1 can improve the reading performance;
- RAID 1 is the highest unit cost in 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 reorganizing the failed data.
RAID 5 – balance between performance and data backup
- N (n > = 3) disks form an array. One piece of data generates n-1 strips and one piece of verification data. A total of N pieces of data are circularly and evenly stored on N disks
- N disks read and write at the same time, with high read performance, but due to the problem of 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.
Raid 6 – more powerful data backup
- N (n > = 4) disks form an array, (n-2) n disk utilization;
- Compared with RAID 5, raid 6 adds a second independent parity information block;
- 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, it has greater “write loss”, so the write performance is poor.
RAID 1 + 0 (mirror first, then stripe)
- After n (even number, n > = 4) disks are mirrored, they are combined into a RAID 0;
- N / 2 disk utilization;
- N / 2 disks are written at the same time, and N disks are read at the same time;
- High performance and high reliability.
RAID 0 + 1 (striping first, mirroring later)
- The read-write performance is the same as that of raid 10;
- Security is lower than raid 10;
- Use less.
2、 Advantages of disk array
3、 Hardware disk array
Disk array introduction
The so-called disk array completes the function of the disk array through the disk array card (shown in the above figure). There is a special chip on the disk array card to handle raid tasks, so it will be better in performance than in price. In many tasks (such as RAID5 parity value calculation), the disk array will not repeatedly consume the I / O bus of the original system, and its performance will be better in theory. In addition, the current medium and advanced disk array cards support hot plug, that is, they can replace damaged disks without shutdown, which is very easy to use in system recovery and data reliability!
Array card introduction
- Array card is a board used to realize raid function
- It is 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:
- For example, raid0, RAID1, RAID5, RAID10, etc. are supported
- Interface type of raid card:
- IDE interface, SCSI interface, SATA interface and SAS interface
Array card cache
- 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 the cache exchanges data with the external data bus.
- The size and speed of cache are important factors directly related to the actual transmission speed of raid card.
- Different raid cards are equipped with different memory capacities at the factory, generally ranging from a few megabytes to hundreds of megabytes.
Software disk array settings
Here is a case to explain the configuration steps in detail:
- Add 4 SCSI hard disks for Linux server;
- Use mdadm software package to build RAID5 disk array to improve the performance and reliability of disk storage.
Add 4 SCSI hard disks to Linux in VMWare
For specific steps, please refer to the third paragraph of this blog: disk management to detect and confirm the new hard disk
Check if the mdadm package is installed
Use RPM – Q mdadm to check, as shown in the figure below, which indicates that the mdadm software has been installed. If not, use Yum install – y mdadm to install.
New disk partition primary partition: type FD
Modify / dev / SDB, / dev / SDC, / dev / SDD, and / dev / SDE disks
Creating RAID 5 devices
#Format mdadm - C - v / dev/md0 - a yes - l5 - n3 / dev/sd[bcd]1 - x1 / dev/sde1
View RAID disk details
#There are two ways to view raid creation progress: [[email protected] ~]# cat /proc/mdstat [[email protected] ~]# mdadm -D /dev/md0 #The creation process is dynamically displayed every 5 seconds [[email protected] ~]# watch -n 5 'cat /proc/mdstat' #Check whether a disk is raid protected [[email protected] ~]# mdadm -E /dev/sdb1
There are two ways to view raid creation progress
Explanation of display content:
[[email protected] ~]# cat /proc/mdstat Personalities : [raid6] [raid5] [raid4] md0 : active raid5 sdd1 sde1(S) sdc1 sdb1 41908224 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU] #MDO: indicates that RAID5 created later contains SDD1, SDE1, SDC1 and sdb1 #Where SDE1 (s) means backup #Uuu in the fourth line: indicates that the first three hard disks are normal
Check whether the / dev / sdb1 disk has been raid.
You can also view it using mdadm – D / dev / md0.
Format and mount the created RAID5
#Format [[email protected] ~]# mkfs -t xfs /dev/md0 #Mount (non permanent) [[email protected] ~]# mount /dev/md0 /opt/
Analog fault detection raid function
Enter the mount directory and create some files and documents
Simulate a disk failure and view the process of re creation.
Create related profiles
Create / etc / mdadm.conf configuration file to facilitate the management of soft RAID configuration, such as start, stop, etc.
[[email protected] opt]# echo 'DEVICE /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1' > /etc/mdadm.conf [[email protected] opt]# mdadm --detail --scan >> /etc/mdadm.conf
Stopping and starting raid
Other common options for the mdadm command:
-r: Remove device -a: Add device -S: Stop raid -A: Start raid mdadm / dev/md0 - f / dev/sdc1 — Set the specified disk as failed mdadm / dev/md0 - r / dev/sdc1 — Remove specified disk mdadm / dev/md0 - a / dev/sdc1 — Add specified disk
Manually delete failed disks and add new disks
Stop and start raid
If you do not add / etc / mdadm and conf configuration files in step 7, you will not be able to start if the configuration files are not scanned after stopping.
mdadm -S /dev/md0 mdadm -As /dev/md0 #-s: Refer to find / Configuration information in the etc / mdadm.conf file