# Common problems

## Duplicate PVs in the system

LVM tries to detect the common sources of duplicates, mdadm RAID and multipath,
there are cases where duplicate PV appears on the system.

There are two solutions to this problem:

* Setting a *global_filter* configuration option.
* Using of *devices_file* (See [lvmdevices(8)](https://man7.org/linux/man-pages/man8/lvmdevices.8.html))

## Device Filtering

*filter* and *global_filter* are meant to be used in two ways:

* as an allow list, listing patterns for devices which will be accepted
* `a|/dev/sdX|`, and rejecting the rest `r|.*|`,
* as a reject list, listing only patterns for devices which will be rejected
* `r|/dev/sdX|`,

Even though there are situations where it works, mixing reject and accept
patterns is not recommended.

