基础知识 -- Linux 逻辑卷管理技术2

怎样从VG中移走PV ?
https:// svn.wso2.org //repos // wso2 // tags // wsas // java // 3.2.1 //
例如将/dev/sdb1从逻辑卷中移出:
linux-0eob:/ # pvmove /dev/sdb1
/dev/sdb1: Moved: 100.0%

linux-0eob:/ # pvscan
  PV /dev/sdb1   VG vg0   lvm2 [52.00 MB / 52.00 MB free]
  PV /dev/sdb2   VG vg0   lvm2 [52.00 MB / 32.00 MB free]
  PV /dev/sdb3   VG vg0   lvm2 [52.00 MB / 52.00 MB free]
  Total: 3 [156.00 MB] / in use: 3 [156.00 MB] / in no VG: 0 [0   ]
从vg0 中移走pv
linux-0eob:/ # vgreduce vg0 /dev/sdb1

  Removed "/dev/sdb1" from volume group "vg0"
再一次查看:
linux-0eob:/ # pvscan
  PV /dev/sdb2   VG vg0             lvm2 [52.00 MB / 32.00 MB free]
  PV /dev/sdb3   VG vg0             lvm2 [52.00 MB / 52.00 MB free]
  PV /dev/sdb1                      lvm2 [54.88 MB]
  Total: 3 [158.88 MB] / in use: 2 [104.00 MB] / in no VG: 1 [54.88 MB]
这样/dev/sdb1就变成自由分区了

怎样指定vg中逻辑块的大小 ?
我们可以使用vgcreate的-s选项指定逻辑块大小,这样可以支持更大的逻辑卷
linux-0eob:/ # vgcreate vg1 -s 8M /dev/sdb1
  Volume group "vg1" successfully created
linux-0eob:/ # vgdisplay vg1
  --- Volume group ---
  VG Name               vg1
  System ID            
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  1
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                0
  Open LV               0
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               48.00 MB
  PE Size               8.00 MB
  Total PE              6
  Alloc PE / Size       0 / 0  
  Free  PE / Size       6 / 48.00 MB
  VG UUID               UWko2s-q9Qp-ybSZ-ZHJr-1FHl-R60q-8jzaR5

在vg1上创建逻辑卷
linux-0eob:/ # lvcreate -n lvdata2 -l 2 vg1
  Logical volume "lvdata2" created
linux-0eob:/ # lvdisplay
  --- Logical volume ---
  LV Name                /dev/vg0/lvdata
  VG Name                vg0
  LV UUID                tYWFX0-Msor-q6I3-dZjE-W06M-UKyj-McRdpP
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                20.00 MB
  Current LE             5
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0
  
  --- Logical volume ---
  LV Name                /dev/vg1/lvdata2
  VG Name                vg1
  LV UUID                U2y1YP-uHOb-dKh3-pZTP-LFXJ-mOUm-hFZKzZ
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                16.00 MB
  Current LE             2
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1
  
lvcreate 强大的功能还有哪些 ?

-s 选项可以备份lv中的数据,--snapshots;可以实时捕捉数据的变化.
    但是这种方式只能在负载不高的情形下进行.
linux-0eob:/ # lvcreate -n snap -s -l 4 /dev/vg1/lvdata2
  Logical volume "snap" created
这样/dev/vg1/lvdata2 中的内容会与 /dev/vg1/snap下的数据是实时同步的

如何转换逻辑卷的状态 ?
linux-0eob:/ # lvscan
  ACTIVE            '/dev/vg0/lvdata' [20.00 MB] inherit
  ACTIVE   Original '/dev/vg1/lvdata2' [16.00 MB] inherit
  ACTIVE   Snapshot '/dev/vg1/snap' [32.00 MB] inherit
linux-0eob:/ # vgchange -an vg0
  Can't deactivate volume group "vg0" with 1 open logical volume(s)
linux-0eob:/ # vgchange -an vg1
  0 logical volume(s) in volume group "vg1" now active
linux-0eob:/ # lvscan
  ACTIVE            '/dev/vg0/lvdata' [20.00 MB] inherit
  inactive Original '/dev/vg1/lvdata2' [16.00 MB] inherit
  inactive Snapshot '/dev/vg1/snap' [32.00 MB] inherit

linux-0eob:/ # vgchange -ay vg1
  1 logical volume(s) in volume group "vg1" now active
linux-0eob:/ # lvscan
  ACTIVE            '/dev/vg0/lvdata' [20.00 MB] inherit
  ACTIVE   Original '/dev/vg1/lvdata2' [16.00 MB] inherit
  ACTIVE   Snapshot '/dev/vg1/snap' [32.00 MB] inherit