According to the knowledge base, you can expand a Synology volume or storage pool in these ways:
1. Expand a volume directly
- If the volume is on a storage pool with multiple volume support, and the storage pool has enough free capacity, you can expand the volume by changing its size.
- If the volume is on a storage pool without multiple volume support, you must expand the storage pool first. [1]
2. Expand by adding new drives
- This is supported when the RAID type allows it. The knowledge base mentions:
- RAID 1
- RAID 5
- RAID 6
- RAID TP [10], [11]
- The volume/storage pool must be in a healthy state, and you need at least one available healthy drive that is:
- in the Synology compatibility list,
- equal to or larger than the smallest drive,
- the same drive type as the others. [10], [11]
- In a Synology High Availability cluster, only RAID 5, RAID 6, RAID F1 are listed for adding new drives. [14]
3. Expand by replacing drives with larger ones
- For SHR, RAID 1, RAID 5, RAID 6, RAID 10, and RAID F1, storage pools can be expanded by replacing smaller drives with larger ones. [1]
- Replace drives one by one:
- replace one drive,
- repair the storage pool,
- then replace the next drive. [1], [2], [3]
- In a high-availability cluster, start with the active server and do not remove drives from both servers at the same time. [2], [3]
4. RAID-specific size rule when adding/replacing
- For RAID 5, RAID 6, and RAID F1, the new drive must be equal to or larger than the smallest drive in the storage pool. [12], [13], [15]
5. Older DSM 4.0 guidance
- An older DSM 4.0 guide also describes replacing disks with larger ones, including shutdown/reinstall steps for some RAID types and older models. This is old DSM-era guidance. [4]
If you want, I can also summarize the exact steps for:
- a standard Synology NAS,
- a High Availability cluster, or
- a specific RAID type.
Sources used: [1], [2], [3], [10], [11], [12], [13], [14], [15], [4]