本文章內容：
1. 縮小根目錄
2. 擴容根目錄
參考資料：
XFS是CentOS 7 预装的操作系统，在LVM中XFS只能扩大不能缩小，所以需要利用xfsdump / xfsrestore 工具在必须缩小lvm 的情况下，备份与还原资料。
1. 縮小根目錄
1.1 我們要將根目錄縮小至10G
[root@localhost ~]# df -Th
Filesystem Type Size Used Avail Use% Mounted on
/dev/mapper/centos-root xfs 17G 1.4G 16G 9% /
devtmpfs devtmpfs 478M 0 478M 0% /dev
tmpfs tmpfs 489M 0 489M 0% /dev/shm
tmpfs tmpfs 489M 6.8M 482M 2% /run
tmpfs tmpfs 489M 0 489M 0% /sys/fs/cgroup
/dev/sda1 xfs 1014M 125M 890M 13% /boot
tmpfs tmpfs 98M 0 98M 0% /run/user/0
/dev/sdb1 xfs 20G 33M 20G 1% /data
1.2 安裝xfsdump工具
[root@localhost ~]# yum install xfsdump -y
安裝完xfsdump包後會產生xfsdump和xfsrestore指令：
[root@localhost ~]# rpm -ql xfsdump
/usr/sbin/xfsdump
/usr/sbin/xfsinvutil
/usr/sbin/xfsrestore
...省略
1.3 備份根目錄
我們將根目錄備份到/data目錄。注意，/data目錄需與根目錄是不同的分區，因為等下要縮減根目錄，根目錄會重建。
[root@localhost ~]# xfsdump -f /data/root.dump /
xfsdump: using file dump (drive_simple) strategy
xfsdump: version 3.1.7 (dump format 3.0) - type ^C for status and control
============================= dump label dialog ==============================
please enter label for this dump session (timeout in 300 sec)
-> root_dump #指定備份會話標籤
session label entered: "root_dump"
--------------------------------- end dialog ---------------------------------
xfsdump: level 0 dump of localhost.localdomain:/
xfsdump: dump date: Mon Jul 22 05:24:53 2019
xfsdump: session id: 32b2d15e-827e-4707-9017-3c03eb7cc676
xfsdump: session label: "root_dump"
xfsdump: ino map phase 1: constructing initial dump list
xfsdump: ino map phase 2: skipping (no pruning necessary)
xfsdump: ino map phase 3: skipping (only one dump stream)
xfsdump: ino map construction complete
xfsdump: estimated dump size: 1435976384 bytes
xfsdump: /var/lib/xfsdump/inventory created
============================= media label dialog =============================
please enter label for media in drive 0 (timeout in 300 sec)
-> root #指定設備標籤，就是對要備份的設備做一個描述
media label entered: "root"
--------------------------------- end dialog ---------------------------------
xfsdump: creating dump session media file 0 (media 0, file 0)
xfsdump: dumping ino map
xfsdump: dumping directories
xfsdump: dumping non-directory files
xfsdump: ending media file
xfsdump: media file size 1370257592 bytes
xfsdump: dump size (non-dir files) : 1333849032 bytes
xfsdump: dump complete: 57 seconds elapsed
xfsdump: Dump Summary:
xfsdump: stream 0 /data/root.dump OK (success)
xfsdump: Dump Status: SUCCESS
[root@localhost ~]# ll -h /data/root.dump
-rw-r--r-- 1 root root 1.3G Jul 22 05:25 /data/root.dump #備份的大小與df -h看到的"/"大小差不多
1.4 重開機使用安裝光碟進入rescue模式
1.4.1 進入安裝光碟後進入Troubleshooting
1.4.2 再進入Rescue a CentOS system
1.4.3 出現以下畫面按ENTER鍵
1.4.4 選擇3不要掛載任何系統目錄進入Shell模式
1.5 输入lvm命令，进入lvm界面，依次输入pvscan、vgscan、lvscan三个命令扫描pv、vg、lv相关信息。然后输入lvchange -ay /dev/centos/root（根目錄分区掛載的LVM名称），此命令是激活根目錄分区所在的逻辑卷，输入 quit或exit返回到bash shell界面
提示：提示：lvchange --help可以看幫助。-ay的a是激活的意思，y是yes， 如果不要激活則使用-an。
1.6 縮小根目錄邏輯卷
1.7 執行pvs、vgs、lvs可以發現空了7G容量出來了，/dev/centos/root也變成10G，此時還沒完成，因為縮小根目錄後系統有可能已遭受破壞
1.8 將/dev/centos/root進行xfs格式化，格式化完後掛載至某一目錄
1.9 掛載/dev/sdb1至某一目錄以將剛才的根目錄備份還原至/dev/centos/root
1.10 進行根目錄還原
1.11 輸入exit重啟系統，輸入df -h即可看到根目錄已縮小了
2. 擴容根目錄
2.1 我們要將根目錄擴充
[root@localhost ~]# df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 475M 0 475M 0% /dev
tmpfs 487M 0 487M 0% /dev/shm
tmpfs 487M 14M 473M 3% /run
tmpfs 487M 0 487M 0% /sys/fs/cgroup
/dev/mapper/centos-root 17G 1.8G 16G 11% /
/dev/sda1 1014M 137M 878M 14% /boot
tmpfs 98M 0 98M 0% /run/user/0
2.2 為系統增加一顆硬碟/dev/sdb
[root@localhost ~]# fdisk -l
Disk /dev/sda: 21.5 GB, 21474836480 bytes, 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000ceb3f
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 2099199 1048576 83 Linux
/dev/sda2 2099200 41943039 19921920 8e Linux LVM
Disk /dev/sdb: 21.5 GB, 21474836480 bytes, 41943040 sectors #增加/dev/sdb硬碟
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0xb4e934d0
Device Boot Start End Blocks Id System
/dev/sdb1 2048 41943039 20970496 8e Linux LVM #將/dev/sdb硬碟分割成/dev/sdb1，LVM格式
Disk /dev/mapper/centos-root: 18.2 GB, 18249416704 bytes, 35643392 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk /dev/mapper/centos-swap: 2147 MB, 2147483648 bytes, 4194304 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
2.3 增加PV
2.3.1 執行pvs指令，看到目前只有一個PV
[root@localhost ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda2 centos lvm2 a-- <19.00g 0
2.3.2 執行pvcreate /dev/sdb1，增加第二個PV
[root@localhost ~]# pvcreate /dev/sdb1
Physical volume "/dev/sdb1" successfully created.
[root@localhost ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda2 centos lvm2 a-- <19.00g 0
/dev/sdb1 lvm2 --- <20.00g <20.00g #第二個PV，目前不屬於任何VG
2.4 擴充VG
2.4.1 執行vgs指令，看到目前只有一個VG
[root@localhost ~]# vgs
VG #PV #LV #SN Attr VSize VFree
centos 1 2 0 wz--n- <19.00g 0
2.4.2 執行vgextend centos /dev/sdb1，擴充現有的VG
[root@localhost ~]# vgextend centos /dev/sdb1
Volume group "centos" successfully extended
[root@localhost ~]# vgs
VG #PV #LV #SN Attr VSize VFree
centos 2 2 0 wz--n- 38.99g <20.00g #VG擴充了，有20G還沒使用
2.5 擴充LV
2.5.1 執行lvs指令，看到目前有root、swap兩個LV
[root@localhost ~]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
root centos -wi-ao---- <17.00g
swap centos -wi-ao---- 2.00g
2.5.2 執行lvextend -l +100%FREE /dev/centos/root，將剩餘的VG空間擴充到根目錄
[root@localhost ~]# lvextend -l +100%FREE /dev/centos/root
Size of logical volume centos/root changed from <17.00 GiB (4351 extents) to 36.99 GiB (9470 extents).
Logical volume centos/root successfully resized.
[root@localhost ~]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
root centos -wi-ao---- 36.99g #已擴充
swap centos -wi-ao---- 2.00g
2.6 執行df -Th，可以看到根目錄並沒有長大，需再執行xfs_growfs /dev/centos/root才會對擴充的LV進行xfs格式大小調整
[root@localhost ~]# df -Th
Filesystem Type Size Used Avail Use% Mounted on
devtmpfs devtmpfs 475M 0 475M 0% /dev
tmpfs tmpfs 487M 0 487M 0% /dev/shm
tmpfs tmpfs 487M 7.7M 479M 2% /run
tmpfs tmpfs 487M 0 487M 0% /sys/fs/cgroup
/dev/mapper/centos-root xfs 17G 1.7G 16G 10% / #雖然LV擴充了，但實際上"/"還沒長大
/dev/sda1 xfs 1014M 137M 878M 14% /boot
tmpfs tmpfs 98M 0 98M 0% /run/user/0
[root@localhost ~]# xfs_growfs /dev/centos/root #使用xfs_growfs指令對擴充的LV進行xfs格式大小調整
meta-data=/dev/mapper/centos-root isize=512 agcount=4, agsize=1113856 blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=0 spinodes=0
data = bsize=4096 blocks=4455424, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0 ftype=1
log =internal bsize=4096 blocks=2560, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
data blocks changed from 4455424 to 9697280
[root@localhost ~]# df -Th
Filesystem Type Size Used Avail Use% Mounted on
devtmpfs devtmpfs 475M 0 475M 0% /dev
tmpfs tmpfs 487M 0 487M 0% /dev/shm
tmpfs tmpfs 487M 7.7M 479M 2% /run
tmpfs tmpfs 487M 0 487M 0% /sys/fs/cgroup
/dev/mapper/centos-root xfs 37G 1.7G 36G 5% / #擴充成功
/dev/sda1 xfs 1014M 137M 878M 14% /boot
tmpfs tmpfs 98M 0 98M 0% /run/user/0
