# LVM - Logical Volume Manager for Linux

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## About LVM2
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LVM aka LVM2 refers to the userspace toolset that provide logical volume
management facilities on linux.
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It is reasonably backwards-compatible with the
original LVM1 toolset.
* TODO: Add information about LVM1 metadata format conversion!
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LVM offers more flexibility than using partitions, allowing one to

* grow and, where supported by filesystem, shrink volumes,
* create snapshots of existing volumes,
* mirror data on multiple disks including RAID levels 5 or 6,
* striping data on multiple disks,
* create a read or write cache.

To use LVM2 you need 3 things:

* [device-mapper](https://sourceware.org/dm/) in your kernel (upstream since long ago)
* the userspace device-mapper support library (*libdevmapper*) (part of lvm2)
* and the userspace LVM2 tools.

## Getting LVM

Most of linux distribution offer packaged LVM tools.
Depending on your distribution use

    # RPM based distributions (Fedora):
    yum install lvm2
    # DEB based distributions (Debian, Ubuntu):
    apt-get install lvm2

Tarballs of the userspace LVM2 source code releases are available from [sourceware.org](https://sourceware.org/pub/lvm2/) [ftp](ftp://sourceware.org/pub/lvm2/).

List of official [mirror sites](https://sourceware.org/mirrors.html) (including http and rsync protocols).

### LVM Releases

[[!inline pages="release-notes/2.03.* and !*/template and !*/Discussion and !tagged(draft) and !tagged(pending)" limit=2 rootpage="release-notes"]]

[[More releases|release-notes/index]]

## Getting Started

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TODO: We are missing a lvm(7) man page explaining this, I think it would be a nic addition!
And perhaps so would be a lvmtroubleshooting(7) guide.
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Word of warning first! Even though LVM errs on the side of data safety it is a
tool with low level access and one may seriously harm their data when used
incorrectly!


* Physical Volume (PV) is underlying disk, local or remote, encrypted or even
  a mdadm RAID volume. PV is divided into so called Physical Extents (PE) which
  are a basic allocation unit.
  List PVs using [pvs(8)](https://man7.org/linux/man-pages/man8/pvs.8.html) or
  [pvdisplay(8)](https://man7.org/linux/man-pages/man8/pvdisplay.8.html).

  Make one by running `pvcreate /dev/sdX`.
  See [pvcreate(8)](https://man7.org/linux/man-pages/man8/pvcreate.8.html). This step is optional.
* Volume Group (VG) consisting of one or more PVs is used as a pool from which LVs are allocated.
  List VGs using [vgs(8)](https://man7.org/linux/man-pages/man8/vgs.8.html) or
  [vgdisplay(8)](https://man7.org/linux/man-pages/man8/vgdisplay.8.html).

  Make one by running `vgcreate VGNAME /dev/sdX...`, add PVs to existing one by `vgextend VGNAME /dev/sdX`.
  To use LVM at least one Volume Group must be present on the system.
  See [vgcreate(8)](https://man7.org/linux/man-pages/man8/vgcreate.8.html), and
  [vgextend(8)](https://man7.org/linux/man-pages/man8/vgextend.8.html).
* Logical Volume (LV) is the block device usually visible to user to be used for file system.
  List PVs using [lvs(8)](https://man7.org/linux/man-pages/man8/lvs.8.html) or
  [lvdisplay(8)](https://man7.org/linux/man-pages/man8/lvdisplay.8.html).

  Make one by running `lvcreate [-n LVNAME] -L SIZE VGNAME`, and you are done!
  See [vgcreate(8)](https://man7.org/linux/man-pages/man8/vgcreate.8.html).

## Avoiding Problems

Good start is to avoid using `{--force|-f}` and `{--yes|-y}` options which are
often seen on internet discussions.
there is a possibility of data loss, LVM tools usually ask, so read the prompts
carefully!  Using `--yes` removes these safety.
Also in some cases where it is too dangerous to proceed, e.g. device is used,
LVM refuses to do so, which can be overridden by `--force`.

Second, when resizing and especially when shrinking LVs it is always a good
idea to use `--resizefs` option which ensures the devices are resized in
correct order.

Third, if you still make a mess, never ever run fsck on damaged LV/FS, this is
usually the final blow to your data. It is always better to ask first!


## Documentation

## Resolving Problems

* Backup if possible!
* Search the problem first, check the list of [[common problems|Problems]]
* Never run `fsck` on damaged LV, LV must be recovered first!
* When asking for help describe exactly how the system got corrupted. It really
  does not help trying to cover one's mistakes in such situation, it takes
  longer to get help and also you are likely to get wrong answer making repair
  impossible.

## Reporting Bugs

* When you find a problem there is often something specific about your system.
  If the problem is reproducible run the failing command(s) with verbose flag
  `-vvvv` which gives developers clue where the problem might be.
  There is a [lvmdump(8)](https://man7.org/linux/man-pages/man8/lvmdump.8.html)
  tool to help collect data about your system, block devices and LVM setup.
* Please report upstream bugs or request features in [Red Hat Bugzilla](https://bugzilla.redhat.com/enter_bug.cgi?product=LVM%20and%20device-mapper)

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TODO:
* Add links to other documentation
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* Resolving problems
  * Backup if possible!
  * Newer run fsck! Do the research first!
  * List of Common issues
    * Resizing in wrong order
    * Thin pool running out of space
    * Configuration - duplicates
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  * IRC?

* Reporting Bugs
  * sosreport/lvmdump
  * BZ

* Contributing
  * gitlab MR

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