If you went between architectures (32bit and 64bit), you’ll need to `rrdtool dump`, and implement a bit of batching. Other than that, you should just be able to transfer the RRAs as is. Transfer them a couple of hundred at a time, or as fast as you can manage within the limits of your disk IOPS, and then just have it timed to run between your updates. Took me a shell 3-liner to move 15k RRAs about 2 years ago.