---
layout: default
title: LVM cheat sheet
date: 2023-09-15 22:23 +0200
---
Example commands for common LVM related tasks.

h2. RAID

h3(#convert-lv-to-raid1). Convert existing LV to RAID1

Extend VG containing the LV with additional PV before conversion.
{% highlight bash %}
# vgextend vgdev /dev/nvme0n1p2
# lvconvert --type raid1 --mirrors 1 vgdev/backup /dev/nvme0n1p2
{% endhighlight %}

List currently used devices and sync status:
{% highlight bash %}
# lvs -a -o +devices
{% endhighlight %}


h3. Rebuild RAID1 LV with integrity layer

As of LVM tools 2.03.21(2) (2023-04-21) @man lvmraid@ says:

bq. Integrity limitations
<br><br>
[...] The following are not yet permitted on RAID LVs with integrity: lvreduce,
pvmove, snapshots, splitmirror, raid syncaction commands, raid rebuild.

That means commands like @lvchange --syncaction repair@ or @lvchange --rebuild@
won't work as expected.

If RAID1 with integrity LV requires refresh (partial synchronization) due to
e.g.  device write errors, but both PVs are otherwise available, take the
following steps to fix it:

* remove integrity layer:
{% highlight bash %}
# lvconvert --raidintegrity n vgdev/backup
{% endhighlight %}

* if it is known which PV failed, rebuild it:
{% highlight bash %}
# lvchange --rebuild /dev/sda vgdev/backup
{% endhighlight %}
and re-add integrity layer to finish. Otherwise split RAID1 into single LVs.
@lvchange --synaction repair@ could theoretically refresh RAID1. But due to
lack of integrity layer, it cannot tell which drive contains uncorrupted data,
so the process must be performed manually:
{% highlight bash %}
# lvconvert --splitmirrors 1 --name backup_split vgdev/backup
{% endhighlight %}

* check integrity of both RAID1 parts:
** whether they differ at all:
{% highlight bash %}
# sha512sum /dev/vgdev/backup /dev/vgdev/backup_split
{% endhighlight %}
** if LVs differ, check filesystems:
{% highlight bash %}
# fsck.ext4 -n -f /dev/vgdev/backup
# fsck.ext4 -n -f /dev/vgdev/backup_split
{% endhighlight %}
** once filesystems are fixed and can be mounted, compare file content to
determine which mirror is valid:
{% highlight bash %}
# mount /dev/vgdev/backup /mnt/mirror1
# mount /dev/vgdev/backup_split /mnt/mirror1
# rsync -d /mnt/mirror1 /mnt/mirror2
{% endhighlight %}

* finally remove invalid mirror, recreate RAID1 and re-add integrity layer