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?
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
vgchange -ay in order to make vgs available in /dev/mapper again after new os installation.
Commented
Oct 20, 2020 at 22:04
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.
vgchange -ay on red hat forum and it happened to work. I will try the same with ubuntu server.
Commented
Oct 20, 2020 at 23:01
/devmapper is working with a reboot. I have updated my answer.
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
