dd backup by block count

[Loggsie]

@framps

My understanding is by default DD will backup used and unused blocks.

I have a rootfs of 30GB and a volume capacity of up to 236GB. I've kept the rootfs small for two reasons, firstly backup and recovery is quicker and secondly I don't have a need beyond 30GB as I'm running headless.

My situation is, while my backups are heavily compressed with gzip down from 236GB to 10GB, restoring on Windows, which is my preferred way takes well over 4 hours or more to restore.

If raspiBackup where to offer a configuration option when dd backup is chosen to specify the block count, in this case 7864320 (30 x 1024 x 1024/4) this would solve substantial overheads and time plus wear and tear on my NVMe drive.

Can this be something pushed to an updated version please?

Thanks

[framps]

There unfortunately is no way right now to specify the block count. But there exists another option called DEFAULT_DD_BACKUP_SAVE_USED_PARTITIONS_ONLY which calculates the block count of the last byte used by the last defined partition and then uses this block count with dd 😉 Here the option is documented.

I suggest to check also the extension scripts. Maybe there's something there that would be useful to you.

[Loggsie]

Great, I'll take a read through the posted documentation.

I did manage to do it manually, depending on ease vs suggested route I could always run a systemd timer or cron with a script

I used the following

dd if=/dev/nvme0n1 bs=4096 count=7864320 status=progress | gzip -1 > /mnt/ext4/manual.img.gz

[framps]

I see. You calculated the end of your last partition by hand. As long as you don't have to extend the root partition that will work. Just let the calculation be done by raspiBackup and any partition extension will be handle for you 😉

Let me know if you face any issue with this option. I frankly suggest to use a different backup type like tar or even much better rsync. But then you're not able to restore the backup from a windows box. Please read this doc

Note: You can improve dd backup speed with this option Default buffer size is 1MB

[Loggsie]

I'll give it a go when I have a spare moment. dd works best for now, but rsync is a viable option, just setting up the restore method without relying upon WSL is a little more hands on, but possible. Tar is out as it adds redundant 512 bytes to each file expanding the img unnecessarily.