Knowledge Center

Hot Spare

A hot spare is a standby drive. When a drive crashes and results in storage pool degradation, the hot spare drive can automatically take the place of the defective drive. This allows the storage pool to repair itself and return to a healthy status in a shorter amount of time.

Note:

  • If there are two crashed drives and only one hot spare drive assigned for repair, the storage pool status will remain as degraded.
  • When a hot spare drive replaces a crashed drive, the hot spare drive becomes part of the storage pool. You should assign another drive as a hot spare drive for storage pool protection.

Before You Start

Requirements:

A hot spare drive can protect a storage pool when the following criteria are met:

  • The RAID type of the storage pool must support drive fault tolerance (i.e., RAID 1, RAID 5, RAID 6, RAID 10, RAID F1, and SHR comprising at least two drives).
  • The capacity of the hot spare drive must be equal to or larger than the capacity of the smallest drive in a RAID 1, RAID 5, RAID 6, RAID 10, or RAID F1 storage pool.
  • The capacity of the hot spare drive must be larger than or equal to the capacity of the largest drive in an SHR storage pool.

Limitations:

Hot spare drives can only protect storage pools comprised of drives of the same type:

  • A storage pool comprised of SATA drives can be protected only by SATA drives assigned as hot spare drives.
  • A storage pool comprised of SAS drives can be protected only by SAS drives assigned as hot spare drives.
  • A storage pool comprised of 4K native drives can be protected only by 4K native drives assigned as hot spare drives.
  • A storage pool comprised of non-4K native drives can be protected only by non-4K native drives assigned as hot spare drives.
  • A storage pool comprised of HDDs can be protected only by HDDs assigned as hot spare drives.
  • A storage pool comprised of SSDs can be protected only by SSDs assigned as hot spare drives.

Note:

  • Starting from DSM 7.0, a storage pool can be created only by drives of the same type. It cannot be created with a mix of both HDDs and SSDs. Likewise, an HDD assigned as a hot spare drive can only replace a defective HDD in a storage pool.
  • If a storage pool created with a mix of HDDs and SSDs is updated from an earlier DSM version to DSM 7.0, then the storage pool can only be repaired manually rather than automatically by hot spare drives when it becomes degraded.

Create Hot Spare Drives

To create a hot spare drive:

Follow the steps below to assign a hot spare drive for storage pool protection:

  1. Go to the Storage page.
  2. Click the Hot Spare button.
  3. Click the Create button.
    Note: This step will not appear if a hot spare drive is created for the first time.
  4. Select the storage pools you want to protect.
  5. Select the drives that you want to assign as hot spare drives.
  6. Click Apply to start creating the hot spare drives.

Once the creation process is complete, you can expand the storage pool information to view the hot spare drives.

Note:

  • When a drive is assigned as a hot spare drive, all data on the drive will be erased. Before assigning a hot spare drive, make sure:
    • The drive has no important data on it.
    • The drive's status is Healthy.
  • We recommend using drives on the Synology Products Compatibility List that are compatible with your Synology NAS model. Using drives not on the list may affect system stability and result in data loss.
  • After a hot spare drive has replaced a crashed drive, the status of the crashed drive will change to Deactivated. This is when you can remove the now deactivated drive safely from the drive slot.

Manage Hot Spare Drives

To view the hot spare drive information:

After a drive has been assigned as a hot spare drive, you can view its information by doing the following:

  1. Go to the Storage page.
  2. Click the Hot Spare button.
  3. Go to the General tab to view the hot spare drive information:
    • Type: Either Dedicated or Shared will be shown. A dedicated hot spare drive will be prioritized during drive replacement.
      • Dedicated: A dedicated hot spare drive is assigned to protect one storage pool.
      • Shared: A shared hot spare drive is assigned to protect more than one storage pool.
    • Hot Spare: This shows which drive serves as a hot spare drive.
    • Drive Type: This shows the hot spare drive type.
    • Available Capacity: This shows the available capacity of the hot spare drive.
    • Protected Storage Pool: This shows the storage pool that is protected by the hot spare drive.

Note:

When multiple hot spare drives are available, they are selected in the following order to replace defective drives in a storage pool:

  1. Dedicated
  2. Located in the same Synology NAS unit as the storage pool
  3. Of the smallest capacity
  4. Others

To manage a hot spare drive:

You can manage a hot spare drive by doing the following:

  1. Go to the Storage page and click the Hot Spare button.
  2. Go to the General tab, select a hot spare drive, and click Edit or Delete to edit or delete it, respectively.

Enable Auto Replacement

To enable Auto Replacement:

Once Auto Replacement is enabled, a hot spare drive will automatically replace a defective drive that is in Critical status. Therefore, you no longer need to worry about storage pool degradation caused by a crashed drive because a defective drive is replaced while its corresponding storage pool is still working normally.

However, note that if a hot spare drive (e.g., Drive 3) is assigned to protect a specific storage pool (e.g., Storage Pool 1), then Drive 3 will only automatically replace the defective drive in Storage Pool 1. That is, Drive 3 will not automatically replace the defective drive in other storage pools.

Auto Replacement is disabled by default. Follow the steps below to enable it:

  1. Go to the Storage page.
  2. Click the Hot Spare button.
  3. Go to the Settings tab and tick the checkbox Enable Auto Replacement when the drive status is "Critical".
  4. Click Apply.

Note:

  • Auto Replacement can only be enabled or disabled after a hot spare drive has been created and assigned for storage pool protection.
  • After a hot spare drive has replaced a crashed drive, the status of the crashed drive will change to Deactivated. This is when you can remove the now deactivated drive safely from the drive slot.
Before You Start
Create Hot Spare Drives
Manage Hot Spare Drives
Enable Auto Replacement