Knowledge Center

Repair a Storage Pool

Storage pool errors may occur as a result of a drive failure or other problems. In most cases, you can follow the steps in this article to diagnose and fix the errors.

Note:

  • We recommend using drives that are compatible with your Synology NAS and are on the Synology Products Compatibility List. Using drives not on the list may affect system stability and result in data loss.
  • If you need to add or remove an M.2 SSD from your Synology NAS, make sure you do so when the system is completely powered off. Refer to the product manual of your Synology NAS model for specific instructions.

Repair a Storage Pool with a Degraded Status

A storage pool becomes Degraded when one or more of its drives becomes defective, but the storage pool remains accessible because no data loss has occurred. You can use the Repair feature to repair a degraded storage pool and return it to a healthy status. Before initiating the repair, replace the defective drives in the storage pool with healthy ones.

Note:

  • The Repair feature is only available for storage pools with data protection, including RAID 1, RAID 5, RAID 6, RAID 10, RAID F1, and SHR comprising of at least two drives.
  • Synology Hybrid RAID (SHR) is available on specific Synology NAS models only.
  • If available drives are assigned as hot spare drives to protect one or more storage pools, then these drives will repair the degraded storage pools automatically. For more information, refer to Hot Spare.

Drive requirements:

Replace the defective drives with healthy drives matching the following criteria:

For RAID 1, RAID 5, RAID 6, RAID 10, and RAID F1 storage pools:
The size of the replacement drive must be equal to or larger than the size of the smallest drive in the storage pool.

For SHR-1 storage pools:
The replacement drive must meet one of the following criteria.

  • The size of the replacement drive is equal to or larger than the size of the defective drive. For example:
    • SHR-1 is composed of 4 TB, 4 TB, 2 TB, and 2 TB drives. If the 4 TB drive becomes defective, the storage pool can be repaired by a drive with a size that is equal to or larger than 4 TB.
    • SHR-1 is composed of 4 TB, 4 TB, 2 TB, and 2 TB drives. If the 2 TB drive becomes defective, the storage pool can be repaired by a drive with a size that is equal to or larger than 2 TB.
  • The size of the replacement drive is equal to or larger than the size of the second-largest drive in the storage pool. For example:
    • SHR-1 is composed of 3 TB, 2 TB, 2 TB, and 1 TB drives. If the 3 TB drive becomes defective, the storage pool can be repaired by a drive with a size that is equal to or larger than 2 TB.
    • SHR-1 is composed of 3 TB, 3 TB, 2 TB, and 1 TB drives. If the 3 TB drive becomes defective, the storage pool can be repaired by a drive with a size that is equal to or larger than 3 TB.

For SHR-2 storage pools:
The replacement drive must meet one of the following criteria.

  • The size of the replacement drive is equal to or larger than the size of the defective drive.
  • The size of the replacement drive is equal to or larger than the size of the fourth largest drive in the storage pool.
    Note: Each SHR-2 array requires a minimum of at least four drives and can withstand two drive failures.

To repair a degraded storage pool:

  1. Go to Storage Manager > Storage and select the storage pool in Degraded status.
  2. Click to view the storage pool information and check the drive status.
  3. Go to the HDD/SSD page to confirm which drive is defective.
  4. Remove the defective drive from your Synology NAS and replace it with a healthy one. If your Synology NAS does not support hot-swapping, power off your device before removing and installing any drives.
    Note: All existing data on the replacement drive will be erased.
  5. After installing the replacement drive, return to the Storage page and select the degraded storage pool.
  6. Click the upper-right icon and select Repair to repair the storage pool.
    Note: The Repair option only appears when a storage pool is degraded.

Note:

  • If the system is taking a long time to repair a storage pool, refer to this article for more information.
  • If the Repair option cannot be selected, refer to this article for troubleshooting steps.

Shorten the Repair Process

Fast Repair is supported on storage pools on which volumes have been created, and can be enabled to accelerate the storage pool repair process. Compared with the traditional rebuild method, Fast Repair skips the unused spaces in a storage pool to accelerate the repair speed and resume RAID protection as fast as possible. This option is enabled by default.

To enable Fast Repair:

  1. Go to Storage Manager > Storage and click the Global Settings button.
  2. Go to the Advanced Repair Settings section and tick the Enable Fast Repair checkbox.
  3. Click Save.

Note:

  • Only storage pools with data protection (i.e., RAID 1, RAID 5, RAID 6, RAID 10, RAID F1, SHR-1, and SHR-2) support Fast Repair.
  • The repair process cannot be accelerated when block-level LUNs on storage pools are being repaired. Block-level LUNs are only supported on DSM 6.1 and versions below, but are still functional when a DSM version is updated to DSM 6.2 and versions above.
  • A storage pool needs sufficient unused space for Faster Repair to accelerate the repair process. If the storage pool usage exceeds 80%, the system will automatically change the repair mode to Regular Repair.
  • You can manually run data scrubbing to optimize a storage pool if the storage pool is in RAID 5, RAID 6, or RAID F1 configuration and if storage pool optimization is not performed after Fast Repair is complete.

Automate the Repair Process

Auto Repair repairs a degraded storage pool automatically once the defective drives have been removed from the drive slots and replaced with new drives, without the hassle of following the steps in the To repair a degraded storage pool section. After the defective drives have been removed from the drive slots, insert the replacement drives in the same drive slots. This option is disabled by default.

To enable Auto Repair:

  1. Go to Storage Manager > Storage and click the Global Settings button.
  2. Go to the Advanced Repair Settings section and tick the Enable Auto Repair checkbox.
  3. Click Save.
  4. Confirm that you want to proceed and click OK.

Note:

  • Auto Repair is not supported on SHR storage pools.
  • Auto Repair is only available on Synology NAS models that support the RAID Group.
  • If Auto Repair has been enabled and hot spare drives have been assigned to a storage pool, the hot spare drives will be used in priority to automatically repair a degraded storage pool.

Troubleshoot a Storage Pool with a Crashed Status

When the status of a storage pool becomes Crashed, you can no longer repair it by yourself. Refer to the following articles for more information on the common volume crash causes and troubleshooting methods:

Repair a Storage Pool with a Degraded Status
Shorten the Repair Process
Automate the Repair Process
Troubleshoot a Storage Pool with a Crashed Status