Setting Up a RAID 5 on a Raspberry Pi 5 with Drives of Different Sizes

The process of setting up a RAID 5 on a Raspberry Pi 5 with disks of different sizes—specifically three 2TB drives, one 1.5TB drive, and one 1TB drive—can be more challenging than with standard hardware. This article explores the feasibility, recommended practices, and potential pitfalls of this DIY project.

Why RAID 5 with Different Drives?

RAID 5 is a widely used storage level where data is distributed across multiple disks, with parity information stored on each disk as well. This setup provides fault tolerance and performance benefits. However, using drives of different sizes can complicate the process and result in suboptimal performance and space usage.

Challenges with Standard RAID 5

Traditional guidelines for RAID 5 recommend using disks of the same size to ensure balanced workload distribution and fairness. In your case, with three 2TB drives, one 1.5TB drive, and one 1TB drive, the minimum shared size (1TB) will be used for the data array, resulting in a total usable space of 4TB. This means the maximum usable space from your 2TB drives will be halved, and the smaller disks will limit the overall size of the RAID array. If one of the larger disks fails, the entire array could be compromised, as the system may not be able to rebuild the lost data.

Alternative Solutions

To maximize the use of available disk space and enhance redundancy, other storage solutions are recommended. Two such alternatives are ZFS and BTRFS, both of which offer better space utilization and data integrity features.

ZFS

ZFS is a modern storage pool framework and file system that comes with built-in features like checksums, snapshots, and copy-on-write semantics. These features ensure better data integrity and make it easier to handle SSD wear and mechanical failures. ZFS is supported by FreeBSD, Linux (via the openzfs project), and Solaris.

To use ZFS on your Raspberry Pi, you would need to install ZFS and then create a storage pool with your drives. Here’s a basic example of how to create a mirrored pool with two 2TB drives and a single 1.5TB drive:

zpool create mypool mirror /dev/sda /dev/sdb raidz1 /dev/sdc /dev/sdd /dev/sde

Note that the above command assumes your drives are named /dev/sda to /dev/sde. Adjust accordingly based on your actual drive names and sizes.

BTRFS

Btrfs is another flexible file system that supports features like snapshots, subvolumes, and checksums. Similar to ZFS, Btrfs can be used to create a storage system that is more resilient and allows for better space utilization. Here’s an example of how to create a Btrfs pool with your drives:

btrfs mkfs -B raid5 /dev/sda /dev/sdb /dev/sdc /dev/sdd /dev/sde

Again, adjust the device names as per your setup.

Using MergerFS for Maximum Utilization

If you still prefer to use a RAID system, the MergerFS utility can be used to combine multiple RAID arrays into one larger namespace. Here’s a theoretical approach to achieve this:

Partition your drives into 500GB partitions: 4 off 2TB drives, 3 off 1.5TB drive, and 2 off 1TB drive. Create 4 separate RAID 5 arrays: each containing one partition from each drive. Union the 4 RAID arrays using MergerFS to create a single virtual drive.

While this method is more complex, it offers a small chance of success. However, the risk of data loss during drive replacement and corruption is high, making it less ideal for most use cases.

SATA and PCIe Connection

If your drives are connected through USB, avoid using any RAID solutions due to the inherent instability of such connections. USB is less robust and more prone to failures, especially when dealing with large datasets.

Avoiding RAID and ZFS/BTRFS Alternatives

Considering the inherent risks and issues with RAID, particularly RAID 5, it is often recommended to avoid it altogether. Instead, ZFS or Btrfs can be used for better space utilization and robust data protection.

For a mirror setup using RAID, you could consider:

Two 1TB and one 1.5TB drives as mirrors for redundancy. A single 2TB drive as RAIDz1 (equivalent of RAID 5) using the remaining 2TB drives for better space utilization.

This setup would provide a total of 4TB usable space and better data redundancy.

Conclusion

Setting up a RAID 5 on a Raspberry Pi 5 with drives of different sizes poses significant challenges. While it is possible to achieve this through complex configurations, alternative storage solutions like ZFS, Btrfs, or even a straightforward mirror setup are more recommended for reliable and efficient data storage.

Always ensure you have regular backups and understand the risks associated with your chosen setup. Regardless of the chosen method, it is crucial to have a recovery plan in place for any unforeseen data loss.