Migrate ds209 (SHR, ext4, 2x 4Tb) to ds920 (SHR, btrfs, no drives)

[Enquiries]

The ds209 still works perfectly already for 13 years on DSM 4.2. Changed to 2x Western Digital Red WD40EFRX 4TB three years ago.
Now I want to migrate to ds920 AND also from ext4 file system to btrfs.
Do you advise to buy new drives for the ds920? Or can I swap the old drives without loss of data?
Thank you very much for your answer.
François

[ed]

Normally you could migrate drives if you run the same DSM.
In this case you may need to use hyper backup or migration assistant https://www.synology.com/en-uk/dsm/feature/migration
If you want to keep those drives, you could move one drive at a time if it is in RAID1 mode.

I hope this helps.