What is the proper way of backing up raid

Question

I have a two disk server where root is on a mirrored LVM volume, while /boot and /boot/efi are RAID1 partitions.

I want to fully backup my server, so that when a disaster happens (both disks fail, or the entire server is gone) I can recover quickly with the least downtime. Let us assume that during the recovery we have a new server available with exactly the same specs and two new fresh disks with the same "geometry", i.e. the same total size and sector size.

What I'm planning to do is the following:

• Backup the partition table of both disks with sfdisk -d /dev/XXX > partXXX.bak, so that I can restore it later on the new server with sfdisk /dev/XXX < partXXX.bak.
• Backup LVM metadata using vgcfgbackup, so that I can restore it later using vgcfgrestore.
• Backup the actual data in the LVM volume using a snapshot and rsync or some other backup tool.

Now, I don't have bullet-proof solution for the /boot and /boot/efi partitions. This is what I came up with:

• Use dd to create images of the entire partitions on both disks.
• Possibly compress them using gzip.
• In case of recovery restore entire partition images on both disks using dd (after restoring the partition tables).

After the procedure is completed it should be possible to simply reboot the system and it should work as it did before the disaster, because the contents of the restored disks are byte-to-byte identical (complete with bootloader, superblocks, etc).

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My issues with dd are following:

• Possible data inconsistencies due to taking an image of a live filesystem. I don't expect these partitions to be often actively written to, but to limit the risks I plan to execute sync and then take an image, and repeat the process one more time. If both images are identical it seems safe to assume no writes happened during the first image creation.
• It seems excessive to image the entire partition including the free space. While compressing should help here, and the partitions are not large (1GiB and 200MiB), still the approach with LVM seems smarter.

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My question is the following: is there an mdadm equivalent of vgcfgbackup and vgcfgrestore which could be used to reliably backup non-file metadata such as superblocks and bootloaders, so that during recovery they can be restored and that it only remains to mount the md and rsync data in?

Also am I perhaps missing something in my disaster recovery plan?

Answer 1

Consider Relax And Recover. https://relax-and-recover.org/

It handles encryption (e.g. LUKS) and it handles incremental backups.

Answer 2

dd duplicates UUIDs so if you mount together the original and the copy you will have problems.

Moreover you can't change the UUID of a FAT partition without reformatting and the EFI system partition is indeed FAT.

rsync is not compatible with byte-to-byte identity (ditto copy).

I don't believe in ditto copy. Imagine the cause of disaster is data corruption, ditto copy will preserve the cause of disaster. On the contrary, with high level copying, you have a better chance to fail at the copy stage, so you can react more quickly.

Actually, if the disaster it total destruction you don't mind UUID not being unique. Maybe the strategy is different, depending on what risk you want to cover.