How to replace 2HDD Volume (HBR duplicated) in a 4 bay nas(920)

I got suggested (Synology AI) to make a full hyper backup, but this requires a C@ subscription or a second NAS…

Starting the docker containers causes a file checksum mismatch on a docker container file, and Volume1 becoming readonly.

Preventing to start of the docker containers, prevents triggering the file mismatch, and so keeping a rw RW Volume1

During backup I have some multiple other file checksum mismatches on file which did not trigger a Volume1 becoming readonly (and I have some older backups)

Volume1 is hybrid raid with 1 drive fault tolerance btrfs 5.2 TB 3.3 TB free. And is scrubbed.

So 2 slots in my 4 bay system

3rd slot is empty, and 4th slot is for video surveillance recording ext4-fs.

Surveillance package stopped for now.

Both Volumes and all 3 drives reports Healthy.

Volume1 has 2 WD60EFRX-68L0BN1 6TB

Having 2 new HDDs:

Seagate IronWolf ST6000VN006 6TB

How to replace the Volume1 HDDs?

What is the best way?

1)Take them both out and replace by new? But what about user shares etc….

Can I put back the old volume! as disc3&4 and copy the data to the new Volume?

2)Turn off, Replace one, turn on, rebuild, turn off, replace the other, turn on, rebuild

3)Add a hot spare in the free slot 3, …

replace first and rebuild?

make second (old) hot spare?

…???

Jace Elric

Participant

February 27, 2026 at 8:51 am

The safest way to replace the two drives in your Synology DS920+ is to change them one at a time, not both together. Stop Docker first so the checksum issue doesn’t force the volume into read-only mode. Deactivate one of the old WD drives in Storage Manager, replace it with a new Seagate IronWolf, and run a repair on the storage pool. Once the rebuild finishes and the pool shows healthy, repeat the same steps for the second drive. This keeps your SHR-1 redundancy in place the whole time and preserves your existing shares, users, and settings. Do not remove both drives at once, since SHR with single-drive fault tolerance cannot handle two disks being removed simultaneously.