4.5. Controlling LVM Device Scans with Filters
At startup, the
vgscancommand is run to scan the block devices on the system looking for LVM labels, to determine which of them are physical volumes and to read the metadata and build up a list of volume groups. The names of the physical volumes are stored in the LVM cache file of each node in the system,
/etc/lvm/cache/.cache. Subsequent commands may read that file to avoiding rescanning.
You can control which devices LVM scans by setting up filters in the
lvm.confconfiguration file. The filters in the
lvm.conffile consist of a series of simple regular expressions that get applied to the device names in the
/devdirectory to decide whether to accept or reject each block device found.
The following examples show the use of filters to control which devices LVM scans. Note that some of these examples do not necessarily represent recommended practice, as the regular expressions are matched freely against the complete pathname. For example,
a/loop/is equivalent to
a/.*loop.*/and would match
The following filter adds all discovered devices, which is the default behavior as there is no filter configured in the configuration file:
filter = [ "a/.*/" ]
The following filter removes the cdrom device in order to avoid delays if the drive contains no media:
filter = [ "r|/dev/cdrom|" ]
The following filter adds all loop and removes all other block devices:
filter = [ "a/loop.*/", "r/.*/" ]
The following filter adds all loop and IDE and removes all other block devices:
filter =[ "a|loop.*|", "a|/dev/hd.*|", "r|.*|" ]
The following filter adds just partition 8 on the first IDE drive and removes all other block devices:
filter = [ "a|^/dev/hda8$|", "r/.*/" ]
lvmetaddaemon is running, the
filter =setting in the
/etc/lvm/lvm.conffile does not apply when you execute the
pvscan --cache devicecommand. To filter devices, you need to use the
global_filter =setting. Devices that fail the global filter are not opened by LVM and are never scanned. You may need to use a global filter, for example, when you use LVM devices in VMs and you do not want the contents of the devices in the VMs to be scanned by the physical host.
For more information on the
lvm.conffile, see Appendix B, The LVM Configuration Files and the
lvm.conf(5) man page.