在单机时代,采用单块磁盘进行数据存储和读写的方式,由于寻址和读写的时间消耗,导致I/O性能非常低,且存储容量还会受到限制。另外,单块磁盘极其容易出现物理故障,经常导致数据的丢失。因此大家就在想,有没有一种办法将多块独立的磁盘结合在一起组成一个技术方案,来提高数据的可靠性和I/O性能呢。
在这种情况下,RAID技术就应运而生了。
RAID ( Redundant Array of Independent Disks )即独立磁盘冗余阵列,简称为「磁盘阵列」,其实就是用多个独立的磁盘组成在一起形成一个大的磁盘系统,从而实现比单块磁盘更好的存储性能和更高的可靠性。
RAID0
RAID1
RAID5
RAID6
RAID10
俗称“条带”,它将两个或多个硬盘组成一个逻辑硬盘,每个硬盘最好大小相同,容量是所有硬盘之和,因为是多个硬盘组合成一个,故可并行写操作,写入速度提高,但此方式硬盘数据没有冗余,没有容错,一旦一个物理硬盘损坏,则所有数据均丢失。因而,RAID0 适合于对数据量大,但安全性要求不高的场景,比如音像、视频文件的存储等。
Linux内核中有一个md(multiple devices)模块在底层管理RAID设备,它会在应用层给我们提供一个应用程序的工具mdadm ,mdadm是linux下用于创建和管理软件RAID的命令。
mdadm命令常见参数解释:
[root@yaoguang ~]# lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sda 8:0 0 20G 0 disk sdb 8:16 0 20G 0 disk
[root@yaoguang ~]# mdadm -C -v /dev/md0 -l 0 -n 2 /dev/sda /dev/sdb mdadm: chunk size defaults to 512K mdadm: Defaulting to version 1.2 metadata mdadm: array /dev/md0 started.
[root@yaoguang ~]# mdadm -Ds ARRAY /dev/md0 metadata=1.2 name=yaoguang:0 UUID=6c29ef17:0f0def7e:0561705d:fdecc6c0
[root@yaoguang ~]# mdadm -Ds > /etc/mdadm.conf [root@yaoguang ~]# cat /etc/mdadm.conf ARRAY /dev/md0 metadata=1.2 name=yaoguang:0 UUID=6c29ef17:0f0def7e:0561705d:fdecc6c0 [root@yaoguang ~]# mdadm -D /dev/md0 /dev/md0: Version : 1.2 Creation Time : Thu Mar 3 21:57:14 2022 Raid Level : raid0 Array Size : 41908224 (39.97 GiB 42.91 GB) Raid Devices : 2 Total Devices : 2 Persistence : Superblock is persistent Update Time : Thu Mar 3 21:57:14 2022 State : clean Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 Layout : -unknown- Chunk Size : 512K Consistency Policy : none Name : yaoguang:0 (local to host yaoguang) UUID : 6c29ef17:0f0def7e:0561705d:fdecc6c0 Events : 0 Number Major Minor RaidDevice State 0 8 0 0 active sync /dev/sda 1 8 16 1 active sync /dev/sdb
[root@yaoguang ~]# fdisk /dev/md0 Welcome to fdisk (util-linux 2.32.1). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Device does not contain a recognized partition table. Created a new DOS disklabel with disk identifier 0x39b83339. Command (m for help): n Partition type p primary (0 primary, 0 extended, 4 free) e extended (container for logical partitions) Select (default p): p Partition number (1-4, default 1): First sector (2048-83816447, default 2048): Last sector, +sectors or +size{K,M,G,T,P} (2048-83816447, default 83816447): Created a new partition 1 of type 'Linux' and of size 40 GiB. Command (m for help): p Disk /dev/md0: 40 GiB, 42914021376 bytes, 83816448 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 524288 bytes / 1048576 bytes Disklabel type: dos Disk identifier: 0x39b83339 Device Boot Start End Sectors Size Id Type /dev/md0p1 2048 83816447 83814400 40G 83 Linux Command (m for help): w The partition table has been altered. Calling ioctl() to re-read partition table. Syncing disks.
[root@yaoguang ~]# mkfs -t xfs /dev/md0p1 log stripe unit (524288 bytes) is too large (maximum is 256KiB) log stripe unit adjusted to 32KiB meta-data=/dev/md0p1 isize=512 agcount=16, agsize=654720 blks = sectsz=512 attr=2, projid32bit=1 = crc=1 finobt=1, sparse=1, rmapbt=0 = reflink=1 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@yaoguang ~]# mkdir /mnt/raid0 [root@yaoguang ~]# mount /dev/md0p1 /mnt/raid0 [root@yaoguang ~]# df | tail -1 /dev/md0p1 41881600 325840 41555760 1% /mnt/raid0
[root@yaoguang ~]# vim /etc/fstab [root@yaoguang ~]# umount /mnt/raid0 [root@yaoguang ~]# df | tail -1 tmpfs 379856 0 379856 0% /run/user/0 [root@yaoguang ~]# mount -av / : ignored /boot : already mounted none : ignored /mnt/raid0 : successfully mounted