Replace Drives to Expand Storage Capacity

When using certain RAID types, you can expand the storage capacity of a volume or disk group by replacing old drives with ones of larger size. This article provides important information regarding the expansion process, as well as an example of how to replace existing drives in order to expand storage capacity.


The procedure described in this article applies to the following RAID types only:

  • SHR
  • RAID 1, RAID 5, RAID 6, RAID 10

If you plan on replacing multiple drives, you must be careful to replace drives one-by-one. After replacing one drive, you must repair the volume or disk group before replacing the next one. For the following RAID types, volume capacity will expand once all drives have been replaced:

  • RAID 1, RAID 5, RAID 6, RAID 10

Before You Start

Before replacing a drive, please see the following notes:

  • Back Up Data: Although the expansion process will not delete any existing data, we strongly recommend backing up your data before proceeding.
  • Volume or Disk Group Status: Before beginning, make sure the status of your volume or disk group is Normal. If not, you must first repair it.
  • Is data still accessible during expansion? Data on your system will be available while expanding volumes or disk groups; although the system may suspend connections temporarily when first starting the process.

SHR (Synology Hybrid RAID)

Because SHR volumes optimize storage capacity based on the number and size of installed drives, please follow the below guidelines in order to properly expand capacity:

  • If the capacity of all existing drives is equal, you must replace at least two drives with larger ones in order to expand storage capacity. For example, if your SHR volume consists of three 2 TB drives, then you must replace at least two drives in order to expand volume capacity.
  • If the capacity of existing drives is different, then the new, replacement drives must be equal to or larger than the largest existing drive. In addition, you must replace smaller drives first in order to optimize capacity usage. For example, if your SHR volume consists of three drives that are 4 TB, 3 TB, and 2 TB, respectively, then your new, replacement drives must be at least 4 TB. In addition, you should replace the 3 TB or 2 TB drives first.

RAID 5 / RAID 6 / RAID 10

When replacing drives of RAID 5 / RAID 6 / RAID 10 volumes or disk groups, the smallest drive should always be replaced first in order to maximize drive usage. The storage capacity of each RAID type is as follows:

  • RAID 5: (number of drives – 1) x (smallest drive size)
  • RAID 6: (number of drives – 2) x (smallest drive size)
  • RAID 10: (number of drives / 2) x (smallest drive size)

For example, if your RAID 5 volume contains three drives that are 4 TB, 3 TB, and 2 TB, respectively, the available capacity of your volume will be 4 TB. If you replace the 4 TB drive or the 3 TB drive, the capacity of the volume will not change. To increase the capacity of your volume, the 2 TB drive must be replaced first.

Replace Drive to Expand Storage Capacity

In the steps below, we will provide an example of replacing the drives of an SHR volume.

To replace drives:

  1. Open Storage Manager.
  2. Go to the Volume to see which existing drive is the smallest.
  3. Turn off your Synology NAS. (Skip this step if your Synology NAS supports hot-swapping.)
  4. Remove the smallest of the member drives and install a new, larger drive.
    Note: To avoid harming yourself or damaging your Synology NAS, please follow the drive installation instructions found in the Hardware Installation Guide for your Synology product.
  5. Turn on your Synology NAS.
  6. Open Storage Manager again.
  7. Go to HDD/SSD to make sure the new drive is recognized.
  8. The status of your volume should be Degraded. Select the volume and click Manage.
  9. Select Repair.
  10. Select the replacement drive to add to the volume. Then follow the steps of the wizard to finish.
  11. Repeat the above process until all desired drives have been replaced with larger ones.