Why Adding Drives to an Existing RAID 5 Array is Not Recommended: Steps for a Safe Upgrade

When dealing with a Synology server, it's crucial to understand the limitations associated with disk arrays, especially when it comes to adding more drives. If you currently have a RAID 5 setup with two out of four drive spaces occupied, you may wonder if it's possible to expand your existing array. Unfortunately, adding more drives to a RAID 5 array is not a straightforward task and can lead to complications and reduced reliability. This article will guide you on why expanding a RAID 5 array is not recommended and offer steps for a safe and effective upgrade.

The Limitations of RAID 5

A RAID 5 array provides a decent balance between disk space and performance, but it has significant limitations, particularly in terms of reliability and redundancy. As the number of drives increases, the risk of data loss also increases, mainly due to the following reasons:

Complexity and Risk of Data Corruption: Adding more drives to a RAID 5 array increases the complexity of error detection and correction. The algorithm used for parity calculation becomes more intricate, leading to a higher risk of data corruption during write operations. Single-Point Failure: In a RAID 5 setup, the failure of a single drive can compromise the entire array. The replacement of a failed drive requires a rebuild process, which can be time-consuming and again potentially introduce data corruption. Performance Degradation: As more drives are added to a RAID 5 array, performance may degrade due to the increased I/O overhead required for parity calculations and error correction.

Recommended Upgrades

For a more reliable and flexible storage solution, consider the following options:

1. RAID 10 for Increased Performance and Reliability

RAID 10 (also known as RAID 1 0) combines the benefits of RAID 1 (mirroring) and RAID 0 (striping). Unlike RAID 5, RAID 10 offers both increased performance and improved data redundancy. RAID 10 can tolerate up to two drive failures without losing data, making it a robust choice for critical applications.

To upgrade to RAID 10, you would need to:

Backup Your Data: It's crucial to back up all data from the existing RAID 5 array to ensure no data is lost during the upgrade process. Create a New RAID 10 Array: You can use all available drives in your Synology server to create a new RAID 10 array. Unlike RAID 5, you can add multiple drives without the risk of data corruption. Restore Your Data: After creating the new RAID 10 array, you can restore the backed-up data to ensure a seamless transition.

Note: You should ensure all drives are the same size to match the RAID 10 requirements. If this is not possible, consider using all available drives and leaving the smallest disk unallocated to achieve the desired RAID 10 array configuration.

2. JBOD (Just a Bunch Of Disks)

JBOD stands for "Just a Bunch of Disks." In a JBOD setup, each drive is treated as a separate volume, allowing you to independently manage and use each drive. JBOD is a simple and flexible storage solution that provides the most flexibility in terms of drive usage and configuration.

To set up JBOD:

Backup Your Data: Similar to the RAID 10 upgrade, ensure all data is backed up before proceeding. Create Separate Volumes: Instead of creating a RAID array, you can create separate volumes for each drive. This approach allows you to manage each drive independently and add or remove drives as needed. Configure the Volumes: Once the separate volumes are created, you can configure each volume as needed, using features like AUFS/MHDDFS to manage file systems and access control.

JBOD can be particularly useful if you want to retain the flexibility of individual drive management without the drawbacks of RAID 5 or 10. However, it's important to note that no redundancy is provided in this setup if a drive fails, so regular backups are crucial.

3. SHR Volumes

SHR (Synology Hybrid RAID) is Synology's default software RAID implementation. It automatically configures two drives as RAID 1 (mirroring) and the remaining drives as RAID 5 or 5 0, depending on the situation. SHR volumes can provide a good balance between performance and data redundancy.

While SHR can handle some level of redundancy, it is not as robust as a dedicated RAID 10 setup for critical applications. However, if you're not dealing with mission-critical data, SHR can still offer a solid solution. To use SHR:

Backup Your Data: Always back up your data before making any changes to the storage configuration. Create SHR Volumes: You can use the Synology DiskStation Manager to create SHR volumes, which will handle the RAID configuration automatically. Monitor and Maintain: Regularly monitor the health of your SHR volumes and ensure that your disk backups are up to date.

SHR is particularly useful for users who are not technically inclined, as it simplifies the process of managing multiple drives and provides some level of data protection without the complexity of manually configuring RAID arrays.

Conclusion

Adding more drives to an existing RAID 5 array is not recommended due to the increased risk of data corruption and the complexity of managing the array. Instead, consider upgrading to RAID 10, JBOD, or using SHR Volumes for a more reliable and flexible storage solution. Whether you choose one of these options, always ensure that you back up your data before making any changes to your storage configuration.

Key Takeaways

RAID 5 can become unstable and unreliable as more drives are added. RAID 10 is a more robust solution with better performance and redundancy. JBOD allows for independent management of each drive, providing maximum flexibility. SHR Volumes offer a simple way to manage multiple drives with automatic RAID configuration.

Further Reading

For a deeper understanding of RAID-like systems and their suitability for home NAS, you may find the following resources helpful:

Comparison of RAID-like Systems for a Home NAS by Wouter Dullaert When No Redundancy Is More Reliable - The Myth of Redundancy by De Graeve

By following these recommendations and considering the appropriate storage solutions, you can ensure better reliability, performance, and flexibility for your Synology server.