Shrinking partition for backup

Question

I have a large SD card ~60G. I expanded Rasbian to the entire disk but now I want to make backups. Preferable backups that aren't 60G. How do those with large SD cards go about this?

Granted I'm only using a small fraction of the entire card.

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
rootfs           59G  850M   56G   2% /
/dev/root        59G  850M   56G   2% /
devtmpfs        215M     0  215M   0% /dev
tmpfs            44M  248K   44M   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs            88M     0   88M   0% /run/shm
/dev/mmcblk0p1   56M  9.7M   47M  18% /boot

Answer 1

You can pipe dd backups into gzip, as the blocks are 0 when unused they are highly compressible.

ssh [email protected] sudo dd bs=4M if=/dev/mmcblk0 | gzip -c > raspberry_dd_4M.img.gz

or from a linux card reader

dd if=/dev/sdc bs=4M | gzip > rasppi_4M.img.gz

and the obligatory recovery command

gunzip -dc /home/user/raspberry_dd_4M.img.gz | dd bs=4M of=/dev/sdc

I took the above from a blog post I wrote in June 2013

Answer 2

You also can use tar to backup your root and boot partition. tar will backup only used space.

To backup the root partition you can use following command:

tar -cvpzf /root.tar.gz --exclude=/root.tar.gz --one-file-system / 

To backup the boot partition you can use following command:

tar -cvpzf /boot.tar.gz --exclude=/boot.tar.gz --one-file-system /boot

Answer 3

Another alternative is to use pishrink

PiShrink is a bash script that automatically shrinks a pi image that will then resize to the max size of the SD card on boot. This will make putting the image back onto the SD card faster and the shrunk images will compress better.

The algorithm mounts the image on a loop device, executes e2fsck, calculates the minimum space required by the second partition, adds some spare space and finally executes resize2fs to shrink the second partition to the calculated minimum size.

Answer 4

While not exactly answering your question it still might help. There are tools available - such as partimage - making compressed images of partitions. So no matter how large a partition is, the image size will be mainly influenced by the disk usage.

On a side not however: partimage is not working on ext4 or btrfs filesystems; is doing no defragmentation before saving an image; and needs the filesystem to be unmounted prior to saving.

Answer 5

There's a ready made solution to this question: the script only backs up used space and can be done whilst running on the Pi you want to back up!

https://learn.adafruit.com/adafruit-raspberry-pi-lesson-1-preparing-and-sd-card-for-your-raspberry-pi/make-a-backup-image