/dev/sdb2, sdc2 是两个pv，目前有一个lv叫swap，在sdb2上，大小是5120个PE。现在想把后2560个PE挪到sdc2上，但是操作失败了。
# pvdisplay -m
—- Physical volume —-
PV Name /dev/sdb2
VG Name system
Physical extent 232962 to 238081:
Logical volume /dev/system/swap
Logical extents 0 to 5119
Physical extent 238082 to 238463:
FREE
—- Physical volume —-
PV Name /dev/sdc2
VG Name system
Physical extent 232962 to 238463:
FREE
# pvmove /dev/sdb2:235522-238081 /dev/sdc2:235904
Insufficient free space: 2560 extents needed, but only 0 available
Unable to allocate mirror extents for system/pvmove0.
Failed to convert pvmove LV to mirrored
# pvmove /dev/sdb2:235522-238081 /dev/sdc2:235904-238463
Insufficient free space: 2560 extents needed, but only 0 available
Unable to allocate mirror extents for system/pvmove0.
Failed to convert pvmove LV to mirrored