# Raspberry Pi 4-Based NAS Using USB-Connected Disks

Our little DNS-323 has been rock solid for the last decade but it’s getting long in the tooth and it’s just pokey enough to be annoying when I’m trying to do things on it. After a bit of consideration, I decided to see if I could build one with a Raspberry Pi.

It didn’t take a lot of research to find out that the Pi 1 through Pi 3+ aren’t particularly suited for NAS work. They may have the CPU horsepower, but with the on-board Ethernet and USB sharing the same USB2 port, their performance is reportedly not all that great.

The Pi 4, on the other hand, has entirely different hardware; the USB ports (of which there are two USB3 and two USB2) have their own controller, while the on-board Ethernet has its own controller. This makes for an ENORMOUS improvement in the performance of both USB:

and Ethernet:

With numbers like that, I thought it would be worthwhile to try building a little RAID1/mirrored home NAS around a Pi 4. Here’s what I used:

• Raspberry Pi 4, 2GB model, qty 1
• Official Raspberry Pi 4 power supply, qty 1
• 32GB Sandisk UHS-1 MicroSD card, qty 1
• 4TB Western Digital Blue 3.5″ hard drive, qty 2
• Vantec NexStar TX 3.5″ external USB3 enclosure, qty 2
• 5ft Category 5e patch cord, qty 1

I went with mirroring two disks (RAID1), so that is what I’m going to go through here. If you want to set up a single disk, or set up something like a four-disk mirror, or RAID5/6/1+0, you can use the same software I did but you’ll have to do a bit of research into the settings.

Oh, and if you are going to create a RAIDset with more than one disk, make sure they’re all the same size, otherwise the mirror will only be as large as the smallest of the disks that are part of the RAIDset!

I had originally planned to use openmediavault to mirror the disks and create the network shares, but unfortunately it doesn’t support USB-connected disks. That’s what I get for not reading enough before I buy stuff, I suppose. With omv out of the picture, I decided to try mirroring the disks and set up the network shares myself. Here’s how I did it:

Part 1: Set Up Your Raspberry Pi

I’m not going to get into this because there are already a ton of sites out there that will show you how to do this (and describe it better than I can). I built my NAS with the Raspbian Buster Lite image, dated 2020-02-13. Do not use wireless (don’t bother with a wpa-supplicant.conf file), but make sure you enable ssh, go through the raspi-config menu and don’t forget to apt update and upgrade!

Part 2: Assemble And Format The Disks

This part’s pretty easy. Install the hard drives in the enclosures, connect them to your PC, and using the software of your choice, remove any existing partitions on the disks and create a single NTFS partition (or ext4 if your PC is a Linux machine) that uses the entire capacity of the disk. Once that’s done and you get no errors, safely remove the enclosures from your PC.

Part 3: Put Together And Connect Your Hardware

This part’s pretty easy too. Connect the USB disks to the Pi and turn them on. If things are working properly, the physical enclosures and the disks will be present. To check if the Pi sees the enclosures, type lsusb:

To see if the actual spinning hard drives have been detected, type dmesg | grep sda for the first enumerated disk, and dmesg | grep sdb for the second:

Do not go any farther if the output of either of those commands doesn’t look correct, or if the disk capacity listed is different than you expect. Go back, check all of the parts and connections, and try again.

Part 4: Set A Static IP On eth0

You should at this point already have a cable connecting your Pi to your router or a switch. If you’re using wireless… well, I suppose you can do that if you really want or need to, but you’re going to be making your Pi do its work with one foot in a bucket. Use that RJ-45 jack and get yourself some nice clean Gigabit Ethernet goodness.

To set a static IP, use your favourite editor to edit the /etc/dhcpcd.conf file. Make sure to use sudo so you’re editing it as the superuser. Go right to the bottom of the file, and add the following lines:

# NAS Static IP for eth0
interface eth0
static routers=Z.Z.Z.Z
static domain_name_servers=A.A.A.A B.B.B.B

Where:

• X.X.X.X is the static IP address on your network that you want your NAS to be reachable at
• YY is the CIDR representation of your subnet mask (most home or small businesses will be /24)
• B.B.B.B is the IP address for your secondary DNS server (if you have one)

Make sure that you type everything exactly. Even if you only have one router and one DNS server, you still need to type static routers and static domain_name_servers with the “s”.

Once you’ve finished setting the dhcpcd.conf file, reboot your Pi. Once it comes back up, see if you can ping other devices both inside and outside your network. Then try to do another apt update and upgrade to see if your Pi can talk to the Raspbian repositories. If not, go back over the file and make sure the changes you made were saved. Also check to make sure everything is spelled correctly (remember it’s case sensitive).

Part 5: Mirror The Disks

Congratulations! If you’re here, that means you have successfully set up your Raspberry Pi, can see it on the network, and have two hard disks connected via USB. You are now ready to do something not a lot of other people do – use a Raspberry Pi to make a RAIDset out of a pair of USB-connected disks. Fortunately, the software (like the hardware) has made leaps and bounds since the last time I tried it and it’s pretty easy to set up.

First, let’s make sure the right stuff is installed:

sudo apt update
sudo apt install mdadm

Since you already made sure the disks were working in Step 2, you can go ahead and create a RAID1 mirror. In my case, I didn’t care about the partition size so I used the entirety of both disks with the following command:

sudo mdadm --create --verbose /dev/md0 --level=mirror --raid-devices=2 /dev/sda /dev/sdb

In this case, mdadm is being told:

-- create : Make a new RAIDset
-- verbose : Show what’s going on while the command is running
/dev/md0 : The name of the RAID device you’re creating
--level=mirror : Create a mirror (RAID1)
-- raid-devices=2 : How many disks will be used
/dev/sda /dev/sdb : The names of the disks that will be used

Again, this is how I set up my own little two-disk mirror. If you have a different number of disks or want to set up a different kind of RAIDset, the syntax is pretty much the same but the options are different. You may also want to use particular partitions instead of entire disks like I did. Check out the mdadm man page.

You should now see the lights on the enclosures blinking furiously and/or be able to feel/hear the the hard drives doing something. Depending on the kind and size of disks you have and the type of enclosure, creating the mirror and syncing it up may take up to a day. You can check the progress with the following command:

cat /proc/mdstat

which should give you output something like this, which shows you the status of the mirror sync:

Personalities : [raid1]
md0 : active raid1 sda[3] sdb[2]
3096885440 blocks super 1.2 512K chunks 1 near-copies [2/2] [UU]
[>....................] resync = 0.2% (61504/3096885440) finish=398min speed=14298K/sec
unused devices: <none>

Once it’s done, instead of the above, you should see something similar to the following when you run the same command:

pi@PI-0:~ \$ cat /proc/mdstat Personalities : [raid1] md0 : active raid1 sda[1] sdb[2] 3906885440 blocks super 1.2 [2/2] [UU] bitmap: 0/30 pages [0KB], 65536KB chunk

Note the line with the [UU] at the end. Each U represents an active and healthy RAID disk. If you run cat /proc/mdstat and you see a _ (underscore) instead of a U, there’s a problem with a disk that requires your immediate attention.

Now that the RAIDset is built, you need to save its configuration so your Pi knows what to do with it when it boots:

sudo -imdadm --detail --scan >> /etc/mdadm/mdadm.conf
exit

Now confirm it was saved:

cat /etc/mdadm/mdadm.conf

and look for the line that says something like this (obviously your UUID will be different):

ARRAY /dev/md/0 metadata=1.2 UUID=061a78a9:ceadf64b:b124c1d4:7e35ae85 name=PI-0:0

Now reboot your Pi, and once it comes back up, use cat/proc/mdstat and blkid to see if everything’s okay:

Part 6: Create A Filesystem

Now that the disks are mirrored, it’s time to put a filesystem on them. I use ext4, and I’m creating a filesystem on the RAIDset, NOT the physical disks, so the command is:

sudo mke2fs -t ext4 /dev/md0

This may also take a little while. Once it’s done, edit the /etc/fstab file so that the filesystem on the RAIDset will automount at boot. I use the /mnt directory as the mount point, here’s what my fstab file looks like:

Notice that the UUID of the partition is the same as the UUID for /dev/md0 in the output of blkid.

Type the following to see if your fstab file is set up right:

sudo mount -adf

You should see something like this:

In this case, /dev/md0 is mounted at /mnt and everything looks good. The use is at 12% because I’ve already been using the NAS – yours will probably say 0% or 1%.

Now, shut your Pi down, then turn off the disks. Turn on the disks, wait for them to spin up, and boot up the Pi. Run those two commands again and make sure everything looks good before going any further.

Part 7: Set Up A File Share With Samba

Samba is a mature, stable, and very useful batch of software that makes it pretty easy to create simple network shares. It may already be installed, but just to be on the safe side:

sudo apt install samba
sudo apt install samba-common-bin

Once it’s installed, you’re going to need to configure it by editing the /etc/samba/smb.conf file. I’m only going to set up one network share for now, and if you’re new to Samba, I suggest sticking to one share until you’re familiar with it.

Before we edit the file, though, we need to create the directory that Samba will use to share over the network:

sudo mkdir /mnt/NAS_FILEsudo chown pi /mnt/NAS_FILEsudo chgrp users /mnt/NAS_FILE

Do NOT use /mnt as the directory for your file share – always use a directory that resides on the device you’re mounting. If for some reason /dev/md0 doesn’t mount properly, you may end up writing data to and filling up the SD card instead of using the disks!

The default smb.conf file contains a number of examples, including one for a network share and one for a print share. Copy the default file:

sudo cp /etc/samba/smb.conf /etc/samba/smb.conf_OLD

Now, with sudo, use your favourite text editor to open /etc/samba/smb.conf and go to the bottom section of the file, labelled “Share Definitions”. Delete everything in that section and replace it with the following:

[NAS] comment = NAS Fileshare path = /mnt/NAS_FILE browseable = yes read only = no writable = yes create mask = 0775 directory mask = 0775 valid users = pi

So the “Share definitions” section in my smb.conf file looks like this:

Notice how the “valid users” section has the name “pi” in it – you can change that to anyone you’d like (or have more than one user on that line), but for each user on that line, you’ll need to create an account on the Pi for them. I just stuck to the pi user because I wanted to keep things simple to start.

To test your smb.conf file, run the following:

testparm

The “Loaded services file OK” is a good sign that your smb.conf file has no obvious errors in it. If you don’t get that message, go back through the file and make sure everything is spelled properly, etc.

Now, for each user account you want to grant access, you need to run the smbpasswd utility to set them up in Samba. It will ask for a password, and that password really, really should really be different than the password that’s used by the user to log into the Pi itself!

To add someone to the Samba system:

sudo smbpasswd -a USERNAME

To disable someone’s Samba account:

sudo smbpasswd -d USERNAME

To re-enable someone’s Samba account:

sudo smbpasswd -e USERNAME

In my case, I ran:

sudo smbpasswd -a pi

and gave it a password that was different from the password that I use for logging in with the pi user.

At this point, Samba is installed, you’ve created a directory on the RAIDset that Samba will use for the file share, you’ve edited the smb.conf file, ran smbpasswd for every user that’s listed in the smb.conf file, and tested your configuration with testparm. It’s time to restart Samba so it loads the new configuration:

sudo service smbd restart

If you don’t get any messages or errors, things may actually be working!

Part 8: Access Your New NAS

Finally, the payoff – your own home-built NAS! How you will access it depends on the operating system on the computer you want to access it with. If you open your file or network browser, it may automatically show up. Otherwise, you will have to browse to it. Open your file or network browser and browse to the static IP address you set way back in Part 4.

In Windows, it should look something like this:

In Ubuntu, you may have to enter smb:// before the address:

When you try to open the NAS share, you should be prompted for a username and password. The username will be:

localhost\USERNAME, which in my case waslocalhost\pi

…and the password will be whatever you set it to with smbpasswd.

Some of my friends and family may disagree with this statement, but I like it when things are organized. To help with this, I designed and printed a lightweight frame that holds two disks and a Pi, and has several holes for 5mm M3 screws to fasten things like cable management or velcro or whatever to it. Here’s how mine turned out:

I put the model on Thingiverse, it’s at https://www.thingiverse.com/thing:4235287

As for performance… this setup is much more responsive and can transfer files to and from the disks much faster than the old NAS. Disk fragmentation can slow things down, and the old NAS is a decade old, but it was only about half full so that shouldn’t have been too big a problem.

Transfer rates to and from the Pi are faster than my home wireless is, and browsing the directories on the file share is no different than browsing the directories on my PC. Nice and quick.

150Mbps isn’t too shabby at all! The best I could get out of the old NAS was around 70Mbps. Bottom line – a Pi 4 with two external USB3-connected hard drives makes a serviceable and reasonably fast NAS for home or small business use, although there are security considerations that need to be addressed prior to using it out in the real world.

So that’s the deal. I did a bunch of torture testing when I first set things up, and things recovered gracefully. I will do another post soon to discuss how to fix a mirror if there’s a disk failure or if you need to recover the array entirely due to a Pi failure.

I hope you found this useful!

## 10 thoughts on “Raspberry Pi 4-Based NAS Using USB-Connected Disks”

1. fromtheroof says:

what tool are u using to test the transferspeed of the share?
Mine’s low when coping files the it arround 6.5 Mb/s?

1. Hello!

I did copies to and from a Windows PC that has an SSD, and monitored the speed using nload on the Pi and Performance Monitor on the PC.

Are you doing your testing over copper or over wifi? I found that I couldn’t get much more than what you’re seeing out of a regular 2.4GHz wireless connection. Once I switched to the 5GHz band, I was seeing around 70Mbps or so, but when connected to the switch with a cable I got much better numbers.

Have a good day!

2. Ronald Nutter says:

Mark:

Would like to disagree with you about OpenMediaVault not supporting USB disks. You can use USB hard drives with a little work. While the GUI wont let you setup the drives, once they have been setup, they are manageable/viewable from within the GUI. I set up a USB drive based NAS over a year ago and have had no problems with it. You can setup the drives with a little bit of command line work that I have documented on my YouTube channel.

Thanks,
Ron Nutter
TechBytes with Ron Nutter

1. Hi Ron, thanks for the comment!

Sorry for the delay replying. I admit that when I was tinkering with OMV, I didn’t go any further after the GUI gave an error when I tried to point it to USB-attached disks. It’s good to hear that there’s a way around it (and that you haven’t had any problems after setting them up). The next NAS I build, I may give OMV another try.

Have a good day!

3. Marc says:

Openmediavault works very well with USB Raid. All you have to do is initiate the raid via command line as above. Then you can manage raid, samba, vpn and all other features inside the OMV GUI. Works super well and saves time.

1. Hello Marc! Thanks for the comment!

I’ve had a few people now mention that it’s easy to use USB drives in OMV. I was warned away by the disclaimer on the OMV site that said it doesn’t support USB disks but it’s great to know that option exists!

4. Martin McMerkin says:

First, Thanks for this.
2 problems as I went through, other than just making sure I type all correctly:

Both in Part 5.
When I tried “sudo mdadm –create –verbose /dev/md0 –level=1 –raid-devices=2 /dev/sda1 /dev/sdb1”
it said “mdadm: unexpected failure opening /dev/md0”
I played around, gave up, shut it all down for the night; next day, booted up and it was OK??

When I did the:
“Now reboot your Pi, and once it comes back up, use cat/proc/mdstat and blkid to see if everything’s okay:”
I had to use sudo blkid to see the UUID line

other than that it is all good.
Now I ned to make sure I can manage it and if a disk fails, I can sort it.
Thanks

1. Hi Martin,

Thank you for the comment! I think I ran into the problem you described (or something similar) once when I was building a new RAIDset on a Pi that had previously had another RAIDset configured on it. I couldn’t open /dev/md0 because it was busy looking for the other disks. I don’t remember the details, I wish I’d written them down.

As for using sudo blkid, you’re right. Running it without sudo gets me some information but not every last bit of it. Thank you!

Have a good day – I hope your new NAS does the trick for you!

5. Greg Cole says:

Hey Martin !

I enjoyed reading through the article. I’m curious as to why you decided on spool and spindle drives. Was it for compatibility or storage reasons?

I’m thinking of doing this as well but using SSD’s for the RAID1. I’ve also heard that the Samsung T5 USB drives usually work the best for Raspberry Pi’s. To sum it up I was thinking of building a Raspberry Pi RAID1 redundant NAS with 2 Samsung T5 SSD. Would this be an option of one wanted to utilize the speed of the SSD ?

1. Hi Greg!

Apologies for the delay in my reply.

I went with mechanical disks purely for price/capacity reasons – I don’t do a lot that would thrash disks so I wouldn’t notice the speed improvement all that much.

I’ve also run into trouble TRIMming USB disks. If you do decide to go with SSDs, make sure the USB disk controllers you use support the TRIM commands under Linux.

All that being said, a RAID1 SSD NAS would be pretty sweet. 🙂

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