It sounds like you are considering two additional 4TB drives for a total of three 4TB drives.Hey Everyone,
I am using my Pi4 as a nas. It's connected to a USB 4-slot bay.
At the moment it is as follows:
1. 4 TB drive - for data
2. empty
3. empty
4. 2 TB drive - Time machine drive for my Mac
My 4TB drive is almost full, so I need to get more space. Since I am going to be doing this, I figured I might want to introduce some redundancy. I was thinking of adding 2x 4TB drives. I think I can get 8gb of space, and redundantcy. I could be wrong.
What raid would be ideal? I have never done a raid before, so I am not sure what is best.
I am also open to other suggestions
Using RAID5 on three 4TB drives provides 8TB of space. You need two verified backup copies of your data stored elsewhere before proceeding, since creating a RAID array will erase any data on the existing 4TB drive.
The procedure would then be add the two drives into the extra bays and create a RAID5 array using the three 4TB drives. Make sure not to include the 2TB drive in the array by accident.
After creating the array, update the configuration files in /etc to specify the device name and drives in the array. Wait until the array resilvers. Check
/proc/mdstat
to see how long it will take.
Reboot. Check the array started on reboot with the correct name. Check mdstat again.
The array will be something like md0 but maybe not. Partition the array. Format the partition, for example, as an empty ext4 filesystem. Now copy your data from the backup to the newly created ext4 filesystem. If the first copy of the saved data has errors on restore use the other copy.
The difficulty is making sure you have two verified copies of the data saved somewhere else before proceeding. Two copies is somehow the minimum since the backups will be the only source of data while you reformat the storage on the Pi.
If the data is not important enough to always have two copies, the kitten named Scratchy suggests just deleting it and then you will have 4TB of free space immediately without the need to buy any new disks. Kittens are always trouble.
Statistics: Posted by ejolson — Sat Jan 10, 2026 3:56 am