Disk array RAID
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RAID: Redundant Array of Independent Disks (Redundant Array of Independent Disks)
role: fault tolerance, improved read and write rate
Advantages and Disadvantages of RAID Type Number Utilization
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RAID0 Stripe Set 2 + 100% Fastest read and write rate, fault-tolerant
RAID1 Mirror Set 2 50% Read and write rate average, fault-tolerant
RAID5 with parity Stripe Set 3 + (n-1)/n Fast read and write rate , fault tolerance, allow bad one
RAID6 stripe set with parity double parity dp 4+(n-2)/n fast read and write, fault tolerant, allow two bad
RAID01
RAID10 RAID1 security + RAID0 high speed 4 50% read and write rate Fast, fault-tolerant
RAID50 RAID5 security + RAID0 high-speed 6 (n-2)/n fast read and write rate, fault-tolerant
RAID60 RAID6 security + RAID0 high-speed 8 (n-4)/n high read and write rate, fault-tolerant
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1. The use of RAID in different scenarios
RAID implementation
Hard RAID: Requires RAID card, has its own CPU, fast processing speed, with or without battery
Soft RAID: implemented through operating systems, such as Windows, Linux
2. RAID5 (3 hard drives) + hot backup (1 hard drive)
1. Prepare 4 hard drives
[root@maiya ~]# ll /dev/sd*
brw-rw---- 1 root disk 8, 48 Jan 13 16:07 /dev/sdd
brw-rw---- 1 root disk 8, 64 Jan 13 16:07 /dev/sde
brw-rw---- 1 root disk 8, 80 Jan 13 16:07 /dev/sdf
brw-rw---- 1 root disk 8, 80 Jan 13 16:07 /dev/sdg
2. Create RAID
[root@maiya ~]# yum -y install mdadm //Ensure the mdadm command is available
[root@maiya ~]# mdadm -C /dev/md0 -l5 -n3 -x1 /dev/sd{d,e,f,g }
mdadm: array /dev/md0 started.
-C create RAID
/dev/md0 first RAID device
-l5 RAID5
-n number of RAID members
-x number of hot spares
3. Format, mount
[root@maiya ~]# mkfs.xfs /dev/md0
[root@maiya ~]# mkdir /mnt/raid5
[root@maiya ~]# mount /dev/md0 /mnt/raid5
[root@maiya ~]# cp -rf /etc /mnt/raid5/etc1
4. View RAID information
[root@maiya ~]# mdadm -D /dev/md0 //-D 查看详细信息
/dev/md0:
Version : 1.2
Creation Time : Mon Jan 13 16:28:47 2014
Raid Level : raid5
Array Size : 2095104 (2046.34 MiB 2145.39 MB)
Used Dev Size : 1047552 (1023.17 MiB 1072.69 MB)
Raid Devices : 3
Total Devices : 4
Persistence : Superblock is persistent
Update Time : Mon Jan 13 16:34:51 2014
State : clean Active Devices : 3
Working Devices : 4
Failed Devices : 0
Spare Devices : 1
Layout : left-symmetric
Chunk Size : 512K
Number Major Minor RaidDevice State
0 8 48 0 active sync /dev/sdd
1 8 64 1 active sync /dev/sde
4 8 80 2 active sync /dev/sdf
3 8 96 - spare /dev/sdg5. Simulate a hard drive failure and remove it
Terminal 1:
[root@maiya ~]# watch -n 0.5 'mdadm -D /dev/md0 | tail' //watch keeps checking
Terminal 2:
[root@maiya ~]# mdadm /dev/md0 -f /dev/ sde -r /dev/sde
//simulate broken and remove -f --fail -r --remove
6. Set RAID to take effect after booting
[root@maiya ~]# mdadm -D -s
ARRAY /dev/md0 metadata=1.2 name=sxl1.com:0 UUID=c6761621:8878498f:f5be209e
[root@maiya ~]# mdadm -D -s > /etc/mdadm.conf
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mdadm选项：
-s --scan
-S --stop
-D --detail
-C --create
-f --fail
-r --remove
-n --raid-devices=3
-x --spare-devices=1
-l --level=5
参考：
Update Time : Mon Aug 4 22:47:47 2014
State : clean, degraded, recovering
Active Devices : 2
Working Devices : 3
Failed Devices : 0
Spare Devices : 1
Layout : left-symmetric
Chunk Size : 512KRebuild Status : 3% complete
Name : localhost.localdomain:0 (local to host localhost.localdomain)
UUID : 3df9624c:138a5b3e:2f557132:59a43d04
Events : 41
Number Major Minor RaidDevice State
0 252 16 0 active sync /dev/vdb
3 252 64 1 spare rebuilding /dev/vde
4 252 48 2 active sync /dev/vdd