Converting and Shrinking RAID Arrays: From SHR to RAID5 on Synology DSM 7.2

[Andy]

Introduction​

Transitioning from Synology Hybrid RAID (SHR) to RAID5 can streamline your storage configuration and improve data redundancy. Here’s my experience merging multiple volumes from SHR into a single RAID5 volume using Synology DiskStation Manager (DSM) 7.2.

Initial Setup​

My initial setup consisted of six 8 TB HDDs configured in SHR, spread across multiple volumes in Storage Pool 1. To facilitate the transition without losing data, I added two additional HDDs and set them up as Storage Pool 2 in RAID1. This temporary setup was crucial as it allowed a safe space to migrate data. If extra bays aren't available, consider temporarily removing one HDD to create Storage Pool 2.

Process​

Here’s a step-by-step breakdown of the process:

1. Backup: Ensure all data is backed up using Synology’s Hyper Backup. This utility ensures a seamless restoration process for your data and packages.
2. Volume Management: In DSM 7.2, managing volumes and storage pools involve specific behaviours:
   • When you delete a volume, DSM automatically shifts system configurations to the next available volume within the same storage pool.
   • If all volumes in Storage Pool 1 are deleted, system configurations automatically transfer to the next available volume in Storage Pool 2.
3. Reconfiguration:
   • Delete all volumes in Storage Pool 1.
   • Remove Storage Pool 1 and set up a new Storage Pool 1 configured as RAID5.
4. Final Adjustments: If Storage Pool 2 is no longer needed:
   • Delete Volume 5 in Storage Pool 2.
   • DSM will return system configurations to the newly created RAID5 volume in Storage Pool 1.

Opportunities for Enhancements in the Restoration Process​

While the restoration of 5.5TB of data taking 25 hours exceeded my initial expectations of 16 hours, this experience underscores an opportunity for enhancements that could significantly benefit Synology users, especially in business environments. The introduction of a pause or resume feature would be a valuable addition to the restoration process. This functionality could mitigate risks associated with network interruptions or power outages, allowing for a restoration to pause and resume without starting over. Such an improvement would not only optimise the restoration timeline but also ensure that businesses could have their systems back up and running swiftly, minimising downtime and enhancing operational continuity.

Learnings and observations​

The volume naming conventions in DSM ensure that gaps are filled by renumbering the volumes sequentially. For instance, if you delete previous volumes, the system will fill the gap with the next available volume number. Additionally, it’s important to note that you can delete your main pool’s volumes without losing user settings, passwordless authentication, and all settings in ‘Personal’ by creating a secondary volume on another storage pool. This understanding is crucial for managing and navigating Synology’s DSM environment effectively.

In Synology DSM 7.2, storage pools and volumes behave in a specific manner:

• Volume Creation: In Storage Pool 1, you can create multiple volumes, labelled as Volume 1, Volume 2, Volume 3, and so on.
• System Configuration Management: When a volume is deleted, DSM automatically moves the system configurations to the next available volume within the same storage pool. For example, if Volume 1 is deleted, system settings shift to Volume 2. If you then delete Volume 2, the settings revert back to Volume 1, not Volume 3.
• Storage Pool Deletion: Deleting all volumes in Storage Pool 1 prompts DSM to transfer system configurations to a volume in Storage Pool 2 (e.g., Volume 5). Deleting all volumes in Storage Pool 2 will prompt DSM to move the system configurations back to Volume 1 in Storage Pool 1.

If you attempt to remove the last remaining volume on the NAS, you will receive this message:

Conclusion​

Converting from SHR to RAID5 can significantly enhance your storage infrastructure, combining improved efficiency with robust data protection. The key to a smooth transition is thorough planning, adequate backup, and an understanding of the nuances of DSM’s storage management.

This approach would also be effective if you need to reduce the size of your RAID array, for example, from a six-drive RAID5 to just a three-drive RAID5. This might become necessary as HDD capacities increase and prices decrease over time, allowing for more simplified management and better efficiency, and giving you the potential for better array expansion in the future.