If you follow the steps above you will effectively discard all the existing checksums for the files on d1 and d2 and generate them anew. From an integrity pov it’s not optimal.

Better to:

1. replace d1 with the new larger disk
2. move all files from d2 to the new larger disk (see ‘How can I safely move files from one disk to another?’ in the FAQ)

This is an outline, not step-by-step. If OP wants step-by-step for these then ask. But the manual & FAQ covers most things.

SSDs have come down in price steadily. New developments are still contributing to lower price per GB. I have seen SSDs for $30/TB this year.

HDD price has been very stagnant, the slope is almost level. $13.75/TB is a good price at retail. New developments enable larger disk sizes but do not cause a significant lowering of price per GB.

Right now SSD is a under 2.5x the price. Not so long ago it was 8x the price. Unless something unexpected occurs, parity will be reached in 5 years or less.

Once parity is reached - or even if SSD gets to 1.25x the price - I cannot think of a good reason to buy HDD.

https://blocksandfiles.com/wp-content/uploads/2021/01/Wikibon-SSD-less-than-HDD-in-2026.jpg