Raspberry Pi Home Server v2: Backing up the OS partition

Note: This post is part of a series. Each post builds on the previous ones. If you are just trying to add one thing to an existing system that was not built following this series, then I cannot promise that these instructions will work for you, although they probably will. If you’ve started from something other than a non-NOOBS Raspbian image, then you’ll probably need to adjust for that.

Please refer to the series Introduction for a list of all the different posts in the series.

Self-Promotion: I have recorded this series as a screencast for Pluralsight:
(http://www.pluralsight.com/courses/raspberry-pi-home-server)
If you have a Pluralsight subscription, please consider watching it. Reading the instructions is one thing, but watching it done demystifies the whole process.

Thank you!


Now that the Raspberry Pi Home Server is up and running off of the hard drive, we’re presented with a problem. We can’t just take a backup of the SD card anymore. In fact, what’s on the SD card probably shouldn’t change from this point on. All the important stuff is on the OS partition of the hard drive.

In this post, I’ll present a couple different methods for backing up the hard drive using a secondary computer, or just using the Pi itself and a second SD card.

Backing up from a Windows computer

I’ve been using and advocating HDD Raw Copy over Win32DiskImager in this second edition of the Raspberry Pi Home Server series because of its ability to compress the image files on the fly, and that ability can be put to good use here as well. All you need to do is hook the Pi’s hard drive up to your Windows computer, and use HDD Raw Copy to copy the drive to an image file just like you’ve been doing with the SD card. It’s exactly the same process. If you’re using Win32DiskImager, the process is the same, only the resulting image files will be the same size as the drive you’re backing up, which brings me to the downside of this method.

Both HDD Raw Copy and Win32DiskImager are going to want to back up the entire hard drive. Not just the OS partition, but the data partition as well. If you have the space to keep that kind of backup around, then good for you, you can restore the entire server, including the OS and Data partitions as well as all of their contents in one go. It’s going to be slow, and it’s going to take up space, but you can do it.

This is part of the reason I keep my actual shared stuff on a completely separate drive now. I like the separation between the devices that make up the Pi itself, and the stuff that the Pi is sharing. I only have to back up a 120GB drive, and it’s mostly empty space, so my compressed image files are not that large.

If you can build your setup like this, I highly recommend it. If not, then you’ll need to continue reading and decide which is right for you.

Backing up from the Pi itself

If, for some reason, you don’t have access to a full Windows, Mac, or Linux computer, you can back up your hard drive by using another Pi. If you’re stranded alone on a desert island and only have a single Pi with you, then you’ll need to do a little prep work, the first step of which will be establishing a power grid.

Since this is the worst-case scenario, we’ll get it out of the way now. We’re going to create another SD card specifically for making backups. The Raspbian Lite image will have everything we need on it, or you can use a full Raspbian installation too. Just prepare another SD card, exactly like we did in “Installing the OS“, and then proceed to the “Backing up from Linux” section.

Backing up from Mac OS

Mac OS is built on top of Unix, which Linux is a sort of clone of, so things work pretty much the same there. You’ll just need do the same thing as the Linux users in the next section.

Backing up from Linux

The process for backing up from Linux is exactly like what you did to create the SD card in the first place, except that you’ll be using dd to copy from the Pi’s OS partition to another spot in your filesystem. This could be somewhere on the hard drive of your main computer, but for this demo I’ll be creating an image of the OS partition on the Data partition of the same drive. Just adjust the file paths to match where you want the image and you’re set to go.

Shut down the Pi, and transfer the hard drive to your main computer, or swap SD cards to the new one you created above. If you’re doing this from a single Pi, then I would also take this opportunity to unplug any other drives you might be using, leaving nothing but the system drive attached, and then start up the Pi with the new SD card.

Use blkid to figure out where the Pi’s hard drive got attached (not mounted, mind you).

sudo blkid

In my case, the hard drive shows up at /dev/sda, and the partitions are /dev/sda1 and /dev/sda2, with sda1 being my OS partition, and sda2 being my data partition. If you’re using a separate Linux system, then sda is probably your own hard drive, and the Pi’s drive will be sdb, sdc, sdd, etc.

I’m writing my image to the second partition of the same hard drive, so I’ll need to mount it first so that I can write files to it. Since this is the first time I’m doing this, I’ll also need to create a placeholder directory for the drive to mount at.

sudo mkdir /mnt/data
sudo mount /dev/sda2 /mnt/data

Now, we’ll use the dd command to copy the sda1 partition to sda2 (or wherever you’ve decided to store the image). The dd command is part of “coreutils”, and newer versions have the ability to give you a progress report as they go. See which version you are running.

dd --version

If it says 8.24 or above, you’ll be able to get a status report with the “status=progress” switch. Back up the OS partition like this.

sudo dd bs=1m if=/dev/sd?? of=IMAGEPATH.img status=progress

Unfortunately, Raspbian is still on 8.23 at the time I’m writing this, so status=progress won’t work. If your OS partition is still relatively small, then doing without feedback is a perfectly viable option, so you can proceed like this.

sudo dd bs=1m if=/dev/sd?? of=IMAGEPATH.img

If your OS partition is very large, or you opted to have just one partition, then you’ll probably want some kind of feedback. Install the dcfldd package through apt-get.

sudo apt-get install dcfldd

The syntax for dcfldd is very similar to that of dd, but it will report its progress as it goes.

sudo dcfldd bs=1m if=/dev/sd?? of=IMAGEPATH.img

When the copy is complete, you can shut down the Pi, or safely remove the hard drive card from your main computer, plug it back into the Pi or swap your SD cards back to normal, make sure everything’s hooked back up like it was before, and restart the system.

Restoring from a backup image

If you need to restore your system to a previous state, the process is just the same, but with the “if” and “of” parameters flipped like they were when you created the original SD card. You’ll need to read from the image file and write it to the hard drive partition.

Shut down the system and move the hard drive to the computer that will be doing the restore, or swap to the “backup” SD card if you’re doing this directly from the Pi, and run the dd or dcfldd command as appropriate. Don’t forget to mount the data partition if you’re doing this from the same Pi. You might want to edit the /etc/fstab file so that this happens automatically whenever you’re using your “backup” SD card.

sudo dd bs=1m if=IMAGEPATH.img of=/dev/sd??

or, if you’re doing this from the same Pi

sudo mount /dev/sda2 /mnt/os
sudo dcfldd bs=1m if=/dev/sd?? of=IMAGEPATH.img

Easy, right?

What’s next?

Everything after this point is purely optional. Return to the Introduction, and follow whatever links you want, mixing and matching whatever additional components you want your server to have.

This entry was posted in Computers and Internet, Home Server, Raspberry Pi and tagged , , , . Bookmark the permalink.

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