lvresize -L +XXG [path]
resize2fs [path]
Resizing mounted volumes is limited to growing, you can’t shrink using resize2fs unless the block device is unmounted.
LVM is not only lack of important features, but all this jugglery with [pv|vg|lv][create|remove|reduce..blablabla] doesn't make admins happier.
http://bisqwit.iki.fi/story/howto/undopvremove/
(btw, this fellow has done very well indeed.)
