Mirror pve-root Using LVM RAID1

What this means:

You configure a mirror (RAID1) so that any write to pve-root is also written to sda1. If your NVMe dies, you can still boot from sda1.

🧱 Requirements:

sda1 must be equal to or larger than pve-root (96 GB in your case)
You must convert pve-root into a RAID1 logical volume (LVM mirror)
Some downtime or maintenance mode required

🧰 How-To (Overview Only):

Backup First! (Always)
Check current setup:
- lvdisplay pve/root
Wipe and prep sda1:
- pvcreate /dev/sda
- vgextend pve /dev/sda
Convert pve-root to RAID1:
- lvconvert --type mirror -m1 --mirrorlog core pve/root /dev/sda

This mirrors pve/root from your NVMe disk onto sda.

Option	Meaning
`--type mirror`	Convert the LV to a mirror (RAID1)
`-m1`	Use 1 mirror copy = total of 2 devices
`--mirrorlog core`	Store mirror log in RAM
`pve/root`	The logical volume to convert (your root)
`/dev/sda`	The new disk to mirror onto

Confirm with:
- lvs -a -o +devices

root@pve:~# lvs -a -o +devices
  LV              VG  Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices
  data            pve twi-aotz-- 794.30g             0.01   0.24                             data_tdata(0)
  [data_tdata]    pve Twi-ao---- 794.30g                                                     /dev/nvme0n1p3(26624)
  [data_tmeta]    pve ewi-ao----   8.10g                                                     /dev/nvme0n1p3(229966)
  [lvol0_pmspare] pve ewi-------   8.10g                                                     /dev/nvme0n1p3(232040)
  root            pve mwi-aom---  96.00g                                    100.00           root_mimage_0(0),root_mimage_1(0)
  [root_mimage_0] pve iwi-aom---  96.00g                                                     /dev/nvme0n1p3(2048)
  [root_mimage_1] pve iwi-aom---  96.00g                                                     /dev/sda(0)
  swap            pve -wi-ao----   8.00g                                                     /dev/nvme0n1p3(0)

Optional but smart: Update your bootloader (grub) to know how to boot from either disk:
- update-initramfs -u
- update-grub
- grub-install /dev/sda

✅ Pros:

Real-time mirroring (RAID1)
Transparent failover if one device fails (bootable if configured)

⚠️ Cons:

Adds complexity
If misconfigured, can break boot
Doesn’t protect against file deletion or config mistakes (RAID is not a backup)

how to check the mirror status, detect failures, and know when to do maintenance:

Use `lvdisplay` for more detail:

lvdisplay /dev/pve/root

Look for:

Mirror status: OK (or similar)
If a device has failed, you’ll see something like “failed” or “inconsistent”