lvm2/man/lvreduce.8_des

lvreduce reduces the size of an LV. The freed logical extents are returned
to the VG to be used by other LVs. A copy\-on\-write snapshot LV can also
be reduced if less space is needed to hold COW blocks. Use
\fBlvconvert\fP(8) to change the number of data images in a RAID or
mirrored LV.

Be careful when reducing an LV's size, because data in the reduced area is
lost. Ensure that any file system on the LV is resized \fBbefore\fP
running lvreduce so that the removed extents are not in use by the file
system.

Sizes will be rounded if necessary. For example, the LV size must be an
exact number of extents, and the size of a striped segment must be a
multiple of the number of stripes.

In the usage section below, \fB--size\fP \fISize\fP can be replaced
with \fB--extents\fP \fINumber\fP.  See both descriptions
the options section.