preface
RAID is to combine multiple independent physical hard disks in different ways to form a hard disk group (logical hard disk), so as to provide higher storage performance and data backup technology than a single hard disk
1, RAID disk array introduction
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It is the abbreviation of Redundant Array of Independent Disks, which is called independent redundant disk array in Chinese
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The different ways in which disk arrays are composed are called RAID levels
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Common RAID levels:
RAID0,RAID1,RAID5,RAID6,RAID 1+0
1.1 RAID 0 disk array introduction
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RAID 0 continuously divides data in bits or bytes and reads / writes to multiple disks in parallel, so it has a high data transfer rate, but it has no data redundancy
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RAID 0 simply improves performance and does not guarantee the reliability of data, and the failure of one disk will affect all data
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RAID 0 cannot be used in situations requiring high data security
Disk space utilization: 100%, so the cost is the lowest.
Read performance: read performance of N single disk
Write performance: write performance of N single disk
Redundancy: none. Any disk damage will result in data unavailability.
1.2 introduction to RAID 1 disk array
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Data redundancy is realized through disk data mirroring, and mutual backup data is generated on paired independent disks
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When the original data is busy, the data can be read directly from the mirrored copy, so RAID 1 can improve the reading performance
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RAID1 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
Disk space utilization: 50%, so the cost is the highest.
Read performance: it can only be read on one disk, depending on the faster disk in the disk
Write performance: both disks need to be written. Although they are written in parallel, the performance of a single disk is slow because it needs to be compared.
Redundancy: as long as one disk in any pair of mirrored disks in the system can be used, the system can operate normally even when half of the hard disks have problems.
1.3 introduction to RAID 5 disk array
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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
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N disks read and write at the same time, and the read performance is very high. However, due to the problem of verification mechanism, the write performance is relatively low
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(N-1)/N disk utilization
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High reliability, allowing one disk to be damaged without affecting all data
Disk space utilization: (N-1)/N, that is, only one disk is wasted for parity.
Read performance: (n-1) * the read performance of a single disk, which is close to that of RAID0.
Write performance: the write performance is worse than that of a single disk (this is not very clear, can it be written in parallel?)
Redundancy: only one disk is allowed to be damaged.
1.4 introduction to raid 6 disk array
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N (n > = 4) disks form an array, (N-2)/N disk utilization
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Compared with RAID 5, RAID 6 adds a second independent parity information block
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Two independent parity systems use different algorithms. Even if two disks fail at the same time, it will not affect the use of data
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Compared with RAID 5, it has greater "write loss", so the write performance is poor
Introduction to 1.5 RAID 1+0 disk array
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After n (even number, n > = 4) disks are mirrored, they are combined into a RAID 0
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oN/2 disk utilization
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oN/2 disks are written at the same time, and N disks are read at the same time
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High performance and reliability
Although Raid10 causes 50% disk waste, it provides 200% speed and single disk damaged data security, and can ensure data security when the damaged disks are not in the same Raid1. If one of the disks is broken, the whole logical disk can still work normally
2, Array card introduction
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Array card is a board used to realize RAID function
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It is usually composed of a series of components such as I/O processor, hard disk controller, hard disk connector and cache
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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
2.1 cache of array card
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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
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The size and speed of cache are important factors directly related to the actual transmission speed of RAID card
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Different RAID cards are equipped with different memory capacities at the factory, generally ranging from a few megabytes to hundreds of megabytes
3, Building a soft RAID disk array case
Requirement Description:
- 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
step
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Installing mdadm
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Preparing partitions for RAID arrays
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Add four SCSI hard disks to the Linux server, and use the fdisk tool to divide a 2GB partition respectively, which is / dev/sdb1, / dev/sdc1, / dev/sdd1 and ldev/sde1
Change its type ID to "fd", corresponding to "Linux raidautodetec", indicating that it supports RAID disk arrays -
Create RAID devices and establish file systems
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Mount and use the file system
3.1 check whether the mdadm package is installed
[root@localhost ~]# rpm -q mdadm mdadm-4.0-5.el7.x86_64 Generally, it is installed by default. If it is not installed yum install -y mdadm
3.2 partition using fdisk tool
Divide the new disk devices / dev/ sdb, / dev/sdc, / dev/sdd, / dev/sde into primary partitions sdb1, sdc1, sdd1 and sde1, and change the ID tag number of the partition type to "fd"
fdisk /dev/ sdb fdisk /dev/ sdc fdisk /dev/ sdd fdisk /dev/ sde #Divide the main partitions sdb1, sdc1, sdd1 and sde1, and change the ID tag number of the partition type to "fd" [root@localhost ~]# fdisk -l disk /dev/sdb: 21.5 GB, 21474836480 Bytes, 41943040 sectors Units = a sector of 1 * 512 = 512 bytes Sector Size (logic/Physics): 512 byte / 512 byte I/O size(minimum/optimum): 512 byte / 512 byte Disk label type: dos Disk identifier: 0 xe2dcc4e9 equipment Boot Start End Blocks Id System /dev/sdb1 2048 41943039 20970496 fd Linux raid autodetect disk /dev/sdc: 21.5 GB, 21474836480 Bytes, 41943040 sectors Units = a sector of 1 * 512 = 512 bytes Sector Size (logic/Physics): 512 byte / 512 byte I/O size(minimum/optimum): 512 byte / 512 byte Disk label type: dos Disk identifier: 0 x2167955e equipment Boot Start End Blocks Id System /dev/sdc1 2048 41943039 20970496 fd Linux raid autodetect disk /dev/sda: 64.4 GB, 64424509440 Bytes, 125829120 sectors Units = a sector of 1 * 512 = 512 bytes Sector Size (logic/Physics): 512 byte / 512 byte I/O size(minimum/optimum): 512 byte / 512 byte Disk label type: dos Disk identifier: 0 x0009b938 equipment Boot Start End Blocks Id System /dev/sda1 * 2048 1026047 512000 83 Linux /dev/sda2 1026048 9414655 4194304 82 Linux swap / Solaris /dev/sda3 9414656 125829119 58207232 83 Linux disk /dev/sde: 21.5 GB, 21474836480 Bytes, 41943040 sectors Units = a sector of 1 * 512 = 512 bytes Sector Size (logic/Physics): 512 byte / 512 byte I/O size(minimum/optimum): 512 byte / 512 byte Disk label type: dos Disk identifier: 0 xab6a3c2d equipment Boot Start End Blocks Id System /dev/sde1 2048 41943039 20970496 fd Linux raid autodetect disk /dev/sdd: 21.5 GB, 21474836480 Bytes, 41943040 sectors Units = a sector of 1 * 512 = 512 bytes Sector Size (logic/Physics): 512 byte / 512 byte I/O size(minimum/optimum): 512 byte / 512 byte Disk label type: dos Disk identifier: 0 xfb0dd633 equipment Boot Start End Blocks Id System /dev/sdd1 2048 41943039 20970496 fd Linux raid autodetect
3.3 creating RAID devices
Create RAID5
[root@localhost ~]# mdadm -C -v /dev/md5 -l5 -n3 /dev/sd[b-d]1 -x1 /dev/sde1 mdadm: layout defaults to left-symmetric mdadm: layout defaults to left-symmetric mdadm: chunk size defaults to 512K mdadm: size set to 20954112K mdadm: Defaulting to version 1.2 metadata mdadm: array /dev/md5 started. -C:Indicates new; -v:Displays details of the creation process. /dev/md5: establish RAID5 Name of the. -ayes:--auto，Indicates that if any device file does not exist, it will be created automatically and can be omitted. -l: appoint RAID The level of, l5 Represents creation RAID5. . -n:Specify how many hard disks to create RAID, n3 Indicates that it is created with 3 hard disks RAID. /dev/sd [bcd]1: Specify to use these three disk partitions to create RAID. -x:Specify how many hard disks to use RAID Hot spare disk, x1 Indicates that one free hard disk is reserved for standby /dev/sde1: Specifies the disk to use as a spare
3.4 creating and mounting file systems
[root@localhost ~]# mkfs.xfs /dev/md5
#format
meta-data=/dev/md5 isize=512 agcount=16, agsize=654720 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=0, sparse=0
data = bsize=4096 blocks=10475520, imaxpct=25
= sunit=128 swidth=256 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal log bsize=4096 blocks=5120, version=2
= sectsz=512 sunit=8 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
[root@localhost ~]# mkdir /opt/lz_md5
#Create LZ in opt directory_ md5
[root@localhost ~]# vim /etc/fstab
/dev/md5 /opt/lz_md5 xfs defaults 0 0
#Configure permanent mount
[root@localhost ~]# mount -a
#Refresh fstab
[root@localhost ~]# df -Th
file system type Capacity used available used% Mount point
/dev/sda3 xfs 56G 3.8G 52G 7% /
devtmpfs devtmpfs 898M 0 898M 0% /dev
tmpfs tmpfs 912M 0 912M 0% /dev/shm
tmpfs tmpfs 912M 9.1M 903M 1% /run
tmpfs tmpfs 912M 0 912M 0% /sys/fs/cgroup
/dev/sda1 xfs 497M 167M 331M 34% /boot
tmpfs tmpfs 183M 12K 183M 1% /run/user/42
tmpfs tmpfs 183M 0 183M 0% /run/user/0
/dev/md5 xfs 40G 33M 40G 1% /opt/lz_md5
[root@localhost ~]# mdadm -D /dev/md5
#View RAID disk details
/dev/md5:
Version : 1.2
Creation Time : Thu Aug 12 16:37:27 2021
Raid Level : raid5
Array Size : 41908224 (39.97 GiB 42.91 GB)
Used Dev Size : 20954112 (19.98 GiB 21.46 GB)
Raid Devices : 3
Total Devices : 4
Persistence : Superblock is persistent
Update Time : Thu Aug 12 16:50:28 2021
State : clean
Active Devices : 3
Working Devices : 4
Failed Devices : 0
Spare Devices : 1
Layout : left-symmetric
Chunk Size : 512K
Consistency Policy : resync
Name : localhost.localdomain:5 (local to host localhost.localdomain)
UUID : 0f24eb68:2f549841:4a3ddd16:5208fd7f
Events : 18
Number Major Minor RaidDevice State
0 8 17 0 active sync /dev/sdb1
1 8 33 1 active sync /dev/sdc1
4 8 49 2 active sync /dev/sdd1
3 8 65 - spare /dev/sde1
3.5 fault recovery
[root@localhost /]# mdadm /dev/md5 -f /dev/sdc1
mdadm: set /dev/sdc1 faulty in /dev/md5
#Simulate / dev/sdc1 failure
[root@localhost /]# mdadm -D /dev/md5
#It is found that sde1 has replaced sdc1
/dev/md5:
Version : 1.2
Creation Time : Thu Aug 12 16:37:27 2021
Raid Level : raid5
Array Size : 41908224 (39.97 GiB 42.91 GB)
Used Dev Size : 20954112 (19.98 GiB 21.46 GB)
Raid Devices : 3
Total Devices : 4
Persistence : Superblock is persistent
Update Time : Thu Aug 12 17:01:27 2021
State : clean, degraded, recovering
Active Devices : 2
Working Devices : 3
Failed Devices : 1
Spare Devices : 1
Layout : left-symmetric
Chunk Size : 512K
Consistency Policy : resync
Rebuild Status : 7% complete
Name : localhost.localdomain:5 (local to host localhost.localdomain)
UUID : 0f24eb68:2f549841:4a3ddd16:5208fd7f
Events : 21
Number Major Minor RaidDevice State
0 8 17 0 active sync /dev/sdb1
3 8 65 1 spare rebuilding /dev/sde1
4 8 49 2 active sync /dev/sdd1
1 8 33 - faulty /dev/sdc1
3.6 create / etc / mdadm Conf configuration file
It is convenient to manage the configuration of soft RAID, such as start and stop
[root@localhost ~]# echo ' DEVICE /dev/sdc1 /dev/sdb1 /dev/sdd1 /dev/sde1' > /etc/mdadm.conf [root@localhost ~]# cat /etc/mdadm.conf DEVICE /dev/sdc1 /dev/sdb1 /dev/sdd1 /dev/sde1 [root@localhost ~]# mdadm --detail --scan >> /etc/mdadm.conf [root@localhost ~]#umount /dev/md5 [root@localhost ~]# mdadm -S /dev/md5 mdadm: stopped /dev/md5 [root@localhost ~]# mdadm -As /dev/md5 mdadm: /dev/md5 has been started with 3 drives.
summary
Use different schemes according to different needs; If you only pursue read-write speed without security, use RAID 0; For security and read-write speed, use RAID 10