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Comment by magicalhippo | Hacker News Reader

Windows' Volume Shadow Copy Service[1] allows applications like databases to be informed[2] when a snapshot is about to be taken, so they can ensure their files are in a safe state. They also participate in the restore.

While Linux is great at many things, backups is one area I find lacking compared to what I'm used to from Windows. There I take frequent incremental whole-disk backups. The backup program uses the Volume Shadow Copy Service to provide a consistent state (as much as possible). Being incremental they don't take much space.

If my disk crashes I can be back up and running like (almost) nothing happened in less than an hour. Just swap out the disk and restore. I know, as I've had to do that twice.

[1]: https://learn.microsoft.com/en-us/windows/win32/vss/the-vss-...

[2]: https://learn.microsoft.com/en-us/windows/win32/vss/overview...

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LVM snapshots are copy on write and can be used the same way.

Any backup software that utilizes LVM in this way?

Ie automatically creates a snapshot and sends the incremental changes since previous snapshot to a backup destination like a NAS or S3 blob storage.

wyng backup does this. It uses the device mappers thin_dump tools to allow for incremental backups between snapshots, too:

https://github.com/tasket/wyng-backup

edit: requires lvm thin provisioned volumes

There is also thin-send-recv which basically does the same as zfs send/recv just with lvm:

https://github.com/LINBIT/thin-send-recv

it uses the same functions of the device mapper to allow incremental sync of lvm thin volumes.

Thanks for the pointers, looks very relevant.

It's just such a low-effort peace of mind. Just a few clicks and I know that regardless what happens to my disk or my system, I can be up and running in very little time with very little effort.

On Linux it's always a bit more work, but backups and restore is one of those things I prefer is not too complicated, as stress level is usually high enough when you need to do restore to worry about forgetting some incantation steps.

it depends. Doing a complete disaster recovery of a windows system IMHO can be a real struggle. Especially if you have to restore a system to different hardware, which the system state backup that microsoft offers does not support afaik.

Backing up a linux system in combination with REAR:

https://github.com/rear/rear

and a backup utility of your choice for the regular backup has never failed me so far. I used it to restore linux systems to complete different hardware without any troubles.

For my cases it's been quite easy, but then I've mostly had quite plain hardware so didn't need vendor drivers to recover.

While I've had to recover in anger twice, I've used the same procedure to migrate to new hardware many times. Just restore to the new disk in the new machine, and let Windows reboot a few times and off I went.

REAR looks useful, hadn't seen that before.

I don't think the diffs are usable that way. They're actually more like an "undo log" in that the snapshot space is taken by "old blocks" when the actual volume is taking writes. It's useful for the same reasons as volume shadow copy: a consistent snapshot of the block device. (Also this can be very bad for write performance as any writes are doubled - to snapshot and to to the real device)

Yeah ok, that makes sense. Write performance is a concern, but usually the backups run when there's little activity.

I think block-level snapshots would be very difficult to use this way.

I just make a full dedupped backups from LVM snapshots with kopia, but I've set that up only on one system, on others I just use kopia as-is.

It takes some time, but that's fine for me. Previous backup of 25 GB an hour ago took 20 minutes. I suppose if it only walked files it knew were changed it would be a lot faster.

Thanks, sounds interesting. So you create a snapshot, then let kopia process that snapshot rather than the live filesystem, and then remove the snapshot?

> I suppose if it only walked files it knew were changed it would be a lot faster.

Right, for me I'd want to set it up to do the full disk, so could be millions of files and hundreds of GB. But this trick should work with other backups software, so perhaps it's a viable option.

Exactly so.

Here's the script, should it be of benefit to someone, even if it of course needs to be modified:

    #!/bin/sh
    success=false
    teardown() {
      umount /mnt/backup/var/lib/docker || true
      umount /mnt/backup/root/.cache || true
      umount /mnt/backup/ || true
      for lv in root docker-data; do
        lvremove --yes /dev/hass-vg/$lv-snapshot || true
      done
    
      if [ "$1" != "no-exit" ]; then
        $success
        exit $?
      fi
    }
    
    set -x
    set -e
    teardown no-exit
    trap teardown EXIT
    for lv in root docker-data; do
      lvcreate --snapshot -L 1G -n $lv-snapshot /dev/hass-vg/$lv
    done
    
    mount /dev/hass-vg/root-snapshot /mnt/backup
    mount /dev/hass-vg/docker-data-snapshot /mnt/backup/var/lib/docker
    mount /root/.cache /mnt/backup/root/.cache -o bind
    
    chroot /mnt/backup kopia --config-file="/root/.config/kopia/repository.config" --log-dir="/root/.cache/kopia" snap create / /var/lib/docker
    kopia --config-file="/root/.config/kopia/repository.config" --log-dir="/root/.cache/kopia" snap create /boot /boot/efi
    success=true

Awesome, thanks!

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