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I want to make a NAS storage with Raspberry Pi and attached drive. I would like to create partitions on my drive with LVM, but I'm afraid, that once my sd card with os breaks, I will lose my all data, because as far, as I know, all data needed for LVM to work resides in /etc/lvm on system itself.

My question is - is there any way to restore these settings on new os, once I decide to change sd card for whatever reason?

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It is no problem to access logical volumes from a new installed operating system, e.g. Raspberry Pi OS Buster. Just install

rpi ~$ sudo apt install lvm2

and reboot. That is all what you need to manage, access and mount your LVM volumes on the NAS.

To verify it, I have flashed Raspberry Pi OS (32-bit) Lite based on Debian Buster to a SD Card and installed lvm2. Just without booting I'm able to see the logical volumes on a USB thumb drive:

rpi ~$  sudo pvs
PV         VG       Fmt  Attr PSize   PFree
/dev/sda2  rpi.vg09 lvm2 a--  <29.47g <19.47g

rpi ~$ sudo lvs
LV          VG       Attr       LSize Pool Origin  Data%  Meta%  Move Log Cpy%Sync Convert
root.lv     rpi.vg09 owi---s--- 6.00g
rpi_base.lv rpi.vg09 swi---s--- 4.00g      root.lv

But they are not registered as block devices and cannot be found in /dev/mapper:

rpi ~$ lsblk
lsblk
NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda           8:0    1 29.7G  0 disk
├─sda1        8:1    1  256M  0 part
└─sda2        8:2    1 29.5G  0 part
mmcblk0     179:0    0  3.7G  0 disk
├─mmcblk0p1 179:1    0  256M  0 part /boot
└─mmcblk0p2 179:2    0  3.4G  0 part /

rpi ~$ ls -la /dev/mapper/
total 0
drwxr-xr-x  2 root root      60 Aug 20 11:47 .
drwxr-xr-x 18 root root    3860 Aug 20 11:47 ..
crw-------  1 root root 10, 236 Aug 20 11:47 control

After a reboot I find:

rpi ~$ lsblk
NAME                         MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda                            8:0    1 29.7G  0 disk
├─sda1                         8:1    1  256M  0 part
└─sda2                         8:2    1 29.5G  0 part
  ├─rpi.vg09-root.lv-real    254:0    0    6G  0 lvm
  │ ├─rpi.vg09-root.lv       254:1    0    6G  0 lvm  /mnt
  │ └─rpi.vg09-rpi_base.lv   254:3    0    6G  0 lvm
  └─rpi.vg09-rpi_base.lv-cow 254:2    0    4G  0 lvm
    └─rpi.vg09-rpi_base.lv   254:3    0    6G  0 lvm
mmcblk0                      179:0    0  3.7G  0 disk
├─mmcblk0p1                  179:1    0  256M  0 part /boot
└─mmcblk0p2                  179:2    0  3.4G  0 part /

rpi ~$ ls -la /dev/mapper
total 0
drwxr-xr-x  2 root root     140 Oct 21 10:47 .
drwxr-xr-x 19 root root    3960 Oct 21 10:47 ..
crw-------  1 root root 10, 236 Oct 21 10:47 control
lrwxrwxrwx  1 root root       7 Oct 21 10:47 rpi.vg09-root.lv -> ../dm-1
lrwxrwxrwx  1 root root       7 Oct 21 10:47 rpi.vg09-root.lv-real -> ../dm-0
lrwxrwxrwx  1 root root       7 Oct 21 10:47 rpi.vg09-rpi_base.lv -> ../dm-3
lrwxrwxrwx  1 root root       7 Oct 21 10:47 rpi.vg09-rpi_base.lv-cow -> ../dm-2

rpi ~$ sudo mount /dev/mapper/rpi.vg09-root.lv /mnt
rpi ~$ findmnt /mnt
TARGET SOURCE                       FSTYPE OPTIONS
/mnt   /dev/mapper/rpi.vg09-root.lv ext4   rw,relatime

If you do not want to reboot then you are able to register the block devices direct after installation of lvm2 with:

rpi ~$ vgchange -ay
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  • You are right, but it is worth to mentione, that we have to use command vgchange -ay in order to make vgs available in /dev/mapper again after new os installation. Oct 20 '20 at 22:04
  • @s-kaczmarek I haven't seen so far that I need vgchange on boot up with an attached device. Sometimes I have to use it on dynamically attached usb thumb drives, or when mounting LVM volumes inside an image file.
    – Ingo
    Oct 20 '20 at 22:35
  • I did experiment today in vbox. I created an additional drive, one volume group and two logical volumes. I used alpine as os. I did reinstalled alpine, installed lvm, rebooted and vg was not available in /dev/mapper. I found solution with vgchange -ay on red hat forum and it happened to work. I will try the same with ubuntu server. Oct 20 '20 at 23:01
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    @s-kaczmarek We are on Raspberry Pi here and registering the block devices in /devmapper is working with a reboot. I have updated my answer.
    – Ingo
    Oct 21 '20 at 10:18
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I think you are looking for image-backup

image-backup:

image-backup creates a backup of a running Raspbian system to a standard 'raw' image file that can be written to an SD card or a USB device with Etcher, imageUSB, etc. It will also perform incremental updates to an existing backup image file.

Usage: image-backup [options] [pathto/imagefile for incremental backup]
-h,--help This usage description
-i,--initial pathto/filename of image file [,inital size MB [,added space for incremental MB]]
-n,--noexpand Do not expand filesystem on first run after restore
-o,--options Additional rsync options (comma separated)
-x,--extract Extract image from NOOBS (force BOOT partition to -01 / ROOT partition to -02)"

https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=247568

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