LVM labels and volume group (VG) metadata stored inside physical volume. On Linux system startup vgscan command scan block devices of system and looking for LVM lables. Physical Volume(PV) scanned and Volume Group(VG) list prepared from VG metadata stored in PV. Name of Physical Volumes are stored in /etc/lvm/.cache, subsequent command read /etc/lvm/.cache instead of scanning block devices. LVM cache improve performance as re-scanning of block devices not require.
LVM cache is persistent filter cache. LVM filter control which block device scanned for preparing LVM cache. By default no filter configuration present in LVM configuration file /etc/lvm/lvm.conf, we can put custom filter in configuration file.