resize2fs的问题

calflyok

这是增加lv容量后使用resize2fs的结果，能够在线更新。
[root@localhost ~]# resize2fs /dev/vgtest/lvtest
resize2fs 1.42.9 (28-Dec-2013)
Filesystem at /dev/vgtest/lvtest is mounted on /mnt/lv; on-line resizing required
old_desc_blocks = 5, new_desc_blocks = 5
The filesystem on /dev/vgtest/lvtest is now 593920 blocks long.


下面的是降低lv容量后使用resize2fs的结果，不能在线更新。

[root@localhost ~]# resize2fs /dev/vgtest/lvtest
resize2fs 1.42.9 (28-Dec-2013)
Filesystem at /dev/vgtest/lvtest is mounted on /mnt/lv; on-line resizing required
resize2fs: On-line shrinking not supported

百度了一下，查不到下面错误的原因，求解，谢谢。