Implement software RAID (1) in Redhat Linux AS 4)

Usually, redundant disk arrays (RAID) are used on servers to protect data. High-end servers generally provide expensive hardware RAID controllers. For small and medium-sized enterprises with limited financial strength, using software in Linux to implement the hardware RAID function not only saves investment, but also achieves good results. Why not?
As a server-oriented network operating system, Linux attaches great importance to data security and access speed, linux has implemented support for software RAID since the 2.4 kernel. For background knowledge about RAID, see the appendix. This allows us to avoid buying expensive hardware RAID devices, enhanced disk I/O performance and reliability further reduce the total cost of ownership of the system. Next let's look at a software RAID configuration instance under Redhat Linux AS 4.
System Configuration
Assume that a unit has a new energy collection system that uses the Oracle database. The system has a large amount of data and reads and writes frequently, which requires high real-time performance. at peak times, nearly 40 users are online, high requirements are raised for the disk subsystem of the database server. Due to the tight budget, after multi-party comparison, we finally chose the Linux system as the RAID5 software solution.
The configuration is as follows:
◆ The operating system is RedHat Linux AS 4;
◆ Kernel version 2.6.9-5.EL;
◆ Support for RAID0, RAID1, RAID4, RAID5, and RAID6;
◆ Five 36 gb scsi interface disks, where RedHat AS 4 is installed on the first disk, and the other four constitute RAID 5 to store the Oracle database.
In RedHat AS 4, software RAID is implemented through the mdadm tool. Its version is 1.6.0. It is a single program, which is very convenient and stable to create and manage RAID. Raidtools used in early Linux were not supported in RedHat AS 4 due to its difficult maintenance and limited performance.
Implementation Process
1. Create a partition
Five SCSI disks correspond to/dev/sda,/dev/sdb,/dev/sdc,/dev/sdd, And/dev/sde. The first disk/dev/sda is divided into two zones for installing RedHat AS 4 and performing swap partitioning. The other four disks are divided into only one primary partition, /dev/sdb1,/dev/sdc1,/dev/sdd1,/dev/sde1, and specify the partition type as "fd ", this will enable the Linux kernel to recognize them as RAID partitions and automatically detect and start each boot. Run the fdisk command to create a partition.

# fdisk /dev/sdb

After entering the fdisk command line, Run Command n to create a partition, command t to change the partition type, command w to save the partition table and exit, and command m to help.
2. Create RAID 5
Here, RAID 5 is created on four devices:/dev/sdb1,/dev/sdc1,/dev/sdd1, And/dev/sde1./dev/sde1 is used as the backup device, other devices are active devices. Backup devices are mainly used for backup. Once a device is damaged, it can be immediately replaced by a backup device. Of course, you can also choose not to use the backup device. The command format is as follows:

# mdadm -Cv /dev/md0 -l5 -n3 -x1 -c128 /dev/sd[b,c,d,e]1

The parameters in the Command indicate the following functions: "-C" indicates creating a new array, "/dev/md0" indicates the name of the array device, and "-l5" indicates setting the array mode, you can select 0, 1, 4, 5, and 6, which correspond to RAID0, RAID1, RAID4, RAID5, and RAID6, respectively. Here the mode is set to RAID5; "-n3" indicates the number of active devices in the array. The number of active devices plus the number of standby devices should be equal to the total number of devices in the array. "-x1" indicates the number of backup devices in the array, the current array contains one backup device. "-c128" indicates that the block size is kb and the default value is 64 KB. "/dev/sd [B, c, d, e] 1 "indicates all device identifiers contained in the current array. It can also be separated by spaces. The last one is the backup device.
3. view the array status
When creating a new array or array reconstruction, the device needs to perform synchronization. This process takes some time. You can view the/proc/mdstat file, to display the current status, synchronization progress, and required time of the array.

# more /proc/mdstatPersonalities : [raid5]md0 : active raid5 sdd1[3] sde1[4] sdc1[1] sdb1[0]75469842 blocks level 5, 128k chunk, algorithm 2 [3/2] [UU_][>....................] recovery = 4.3% (1622601/37734912) finish=1.0min speed=15146K/secunused devices:

After the creation or reconstruction is complete, view the/proc/mdstat file again:

# more /proc/mdstatPersonalities : [raid5]md0 : active raid5 sdd1[2] sde1[3] sdc1[1] sdb1[0]75469842 blocks level 5, 128k chunk, algorithm 2 [3/3] [UUU]unused devices:

Through the above content, we can clearly see the status of the current array. The meaning of each part is as follows: the first digit in "[3/3]" indicates the number of devices contained in the array, the second digit indicates the number of active devices. If one device is damaged, the second digit minus 1. "[UUU]" indicates the devices that can be normally used by the current array, if/dev/sdb1 fails, the mark will be changed to [_ UU]. Then the array runs in degraded mode, that is, the array is still available, but there is no redundancy; "sdd1 [2]" indicates that the number of devices contained in the array is n. If the value in square brackets is less than n, it indicates that the device is active. If the value is greater than or equal to n, the device is a backup device. When a device fails, the square brackets of the corresponding device are marked as (F ).
4. Generate a configuration file
The default configuration file of mdadm is/etc/mdadm. conf, which is mainly set to facilitate routine management of arrays. It is not necessary for arrays, but to reduce unnecessary troubles in future management, we should stick to this step.
In the mdadm. the conf file must contain two types of rows: one is the row starting with DEVICE, which indicates the list of devices in the ARRAY; the other is the row starting with ARRAY, it details the name, mode, number of active devices in the array, and UUID of the device. The format is as follows:

DEVICE /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1ARRAY /dev/md0 level=raid5 num-devices=3 UUID=8f128343:715a42df: baece2a8: a5b878e0

The preceding information can be obtained by scanning the system array. The command is:

# mdadm -DsARRAY /dev/md0 level=raid5 num-devices=3 UUID=8f128343:715a42df: baece2a8: a5b878e0devices=/dev/sdb1,/dev/sdc1,/dev/sdd1,/dev/sde1

Use the vi command to edit the/etc/mdadm. conf file in the specified format.

# vi /etc/mdadm.conf