When creating a new volume, start with the smallest drive first!

When expanding capacity by swapping out drives, start with the smallest drive first!

Despite the publicized benefits and ease of management of SHR over classic RAID, a under-highlighted problem is that it still requires new drives to be equal to or greater than existing drives. So when creating a volume with mixed-capacity drives don’t think you can just expand the volume in any order you want.

The SHR FAQ does mention this, however it’s buried in a somewhat long-winded explanation (as opposed to the features it can provide which all start with a resounding “yes!"). It would be nice if the Synology RAID/SHR calculator would mention this to you as you played with drive combinations (it does mumble something in the footnotes about reading other docs though).