扩展系统盘 - 增加系统磁盘大小
系统盘太小时需要扩展系统磁盘，我这里以Azure为例，系统盘默认8G，需要扩展增加磁盘容量。分为两个步骤：
1. 停止实例，调整磁盘大小（实例运行时无法调整，Azure 停止实例注意保存数据）
2. 重新启动实例，扩展磁盘分区大小
第一步不用多说，自己在平台操作即可，我们详细说说第二步：
1. 查看系统盘
[root@azure]# df -h Filesystem Size Used Avail Use% Mounted on devtmpfs 2.0G 0 2.0G 0% /dev tmpfs 2.0G 0 2.0G 0% /dev/shm tmpfs 2.0G 17M 2.0G 1% /run tmpfs 2.0G 0 2.0G 0% /sys/fs/cgroup /dev/sda3 8.0G 2.1G 6.0G 26% / /dev/sda1 1014M 229M 786M 23% /boot /dev/sdb1 7.9G 2.1G 5.4G 28% /mnt/resource tmpfs 394M 0 394M 0% /run/user/1001
系统盘为：/dev/sda3 8.0G 2.1G 6.0G 26% /
2.重新设置分区（数据不会掉的）
[root@azure]# fdisk /dev/sda 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.
输入 p 查看磁盘分区信息
Command (m for help): p Disk /dev/sda: 128 GiB, 137438953472 bytes, 268435456 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disklabel type: dos Disk identifier: 0x53b62a86 Device Boot Start End Sectors Size Id Type /dev/sda1 * 2048 2099199 2097152 1G 83 Linux /dev/sda2 2099200 4196351 2097152 1G 82 Linux swap / Solaris /dev/sda3 * 4196352 268435455 264239104 126G 8e Linux LVM
输入 d 清理分区信息，默认就是系统盘默认分区号3（不同的自己输入系统盘分区号）
Command (m for help): d Partition number (1-3, default 3): Partition 3 has been deleted.
输入 n 新建分区信息：
Command (m for help): n Partition type p primary (2 primary, 0 extended, 2 free) e extended (container for logical partitions)
输入 p 选择 primary类型（然后一直回车）：
Select (default p): p Partition number (3,4, default 3): First sector (4196352-268435455, default 4196352): Last sector, +sectors or +size{K,M,G,T,P} (4196352-268435455, default 268435455): Created a new partition 3 of type 'Linux' and of size 126 GiB. Partition #3 contains a xfs signature. Do you want to remove the signature? [Y]es/[N]o: N
输入 t 修改系统盘为 Linux LVM，我们操作的是默认系统盘分区 3 ， Hex code 输入 8e ：
Command (m for help): t Partition number (1-3, default 3): Hex code (type L to list all codes): 8e
输入 p 查看新分区信息：
Command (m for help): p Disk /dev/sda: 128 GiB, 137438953472 bytes, 268435456 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disklabel type: dos Disk identifier: 0x53b62a86 Device Boot Start End Sectors Size Id Type /dev/sda1 * 2048 2099199 2097152 1G 83 Linux /dev/sda2 2099200 4196351 2097152 1G 82 Linux swap / Solaris /dev/sda3 4196352 268435455 264239104 126G 8e Linux LVM
输入 a 激活分区：
Command (m for help): a Partition number (1-3, default 3): The bootable flag on partition 3 is enabled now.
输入 wr 保存设置：
Command (m for help): wr The partition table has been altered. Syncing disks.
输入 init6 重启机器：
[root@azure]# init 6
----喝水----wait----------wait----------- wait ----------重启完成
3.修改根文件系统的大小为正确值
输入 df 检查容量（容量没变依然8G）：
[root@azure]# df -h Filesystem Size Used Avail Use% Mounted on devtmpfs 2.0G 0 2.0G 0% /dev tmpfs 2.0G 0 2.0G 0% /dev/shm tmpfs 2.0G 17M 2.0G 1% /run tmpfs 2.0G 0 2.0G 0% /sys/fs/cgroup /dev/sda3 8.0G 2.1G 6.0G 26% / /dev/sda1 1014M 229M 786M 23% /boot /dev/sdb1 7.9G 2.1G 5.4G 28% /mnt/resource tmpfs 394M 0 394M 0% /run/user/1001
输入 resize2fs /dev/sda3 修改根文件系统的大小（容量没变依然8G）：
[root@azure]# resize2fs /dev/sda3 resize2fs 1.45.6 (20-Mar-2020) resize2fs: Bad magic number in super-block while trying to open /dev/sda3 Couldn't find valid filesystem superblock.
意料到会报错，因为是xfs系统centos不再支持使用resize2fs修改；因此
输入 xfs_growfs /dev/sda3 即可修改系统盘大小为正确的了
[root@azure]# xfs_growfs /dev/sda3 meta-data=/dev/sda3 isize=512 agcount=4, agsize=524224 blks = sectsz=4096 attr=2, projid32bit=1 = crc=1 finobt=1, sparse=1, rmapbt=0 = reflink=1 data = bsize=4096 blocks=2096896, imaxpct=25 = sunit=0 swidth=0 blks naming =version 2 bsize=4096 ascii-ci=0, ftype=1 log =internal log bsize=4096 blocks=2560, version=2 = sectsz=4096 sunit=1 blks, lazy-count=1 realtime =none extsz=4096 blocks=0, rtextents=0 data blocks changed from 2096896 to 33029888
再次输入 df 检查容量（成功 鼓掌、喝酒 庆祝）：
[root@azure]# df -h Filesystem Size Used Avail Use% Mounted on devtmpfs 2.0G 0 2.0G 0% /dev tmpfs 2.0G 0 2.0G 0% /dev/shm tmpfs 2.0G 17M 2.0G 1% /run tmpfs 2.0G 0 2.0G 0% /sys/fs/cgroup /dev/sda3 126G 2.9G 124G 3% / /dev/sda1 1014M 229M 786M 23% /boot /dev/sdb1 7.9G 2.1G 5.4G 28% /mnt/resource tmpfs 394M 0 394M 0% /run/user/1001
参考：
https://docs.microsoft.com/zh-cn/azure/virtual-machines/linux/expand-disks