Cluster capacity expansion by adding disks

[Carl-Zhou]

I currently have 5 storage servers. Each server is equipped with one 4TB SSD for the operating system, and metadata is also stored on it. Additionally, there are 27 16TB HDDs for storing data, which form a cluster. The EC is set to 4:1.
Now I want to add 5 16TB HDDs to each server for capacity expansion. Is this feasible?
RustFS is running based on the rustfs/rustfs:1.0.0-alpha.79 image.

[pauldev-hub]

Hi @Carl-Zhou ,

You cannot add disks to an existing erasure set — you must add a new server pool.

RustFS (like MinIO it's based on) uses immutable erasure sets. Once a cluster is initialized with 27 disks per server at EC:4:1, that erasure set is fixed. You cannot hot-add 5 disks per server into the existing pool.

The correct way to expand:
New nodes join as new storage pools, and RustFS creates additional Sets to use them. (DeepWiki) You expand by adding a new pool — meaning you add the 5 new disks per server as a separate pool with its own VOLUMES config appended to

RUSTFS_VOLUMES:

Original

RUSTFS_VOLUMES="http://node{1...5}:9000/data/hdd{0...26}"

After expansion (add new pool)

RUSTFS_VOLUMES="http://node{1...5}:9000/data/hdd{0...26} http://node{1...5}:9000/data/hdd{27...31}"

New writes will go to the new pool. Existing data stays on the original pool. Then trigger a rebalance via the admin API to redistribute data.

If this helped you, please mark it as the answer — it helps others in the community who run into the same issue find the solution faster!