I’m thinking of this in terms of hot spares, not cold spares. If you insert a cold spare to replace a disk — yes, you have to write the full disk. If you migr

I’m thinking of this in terms of hot spares, not cold spares. If you insert a cold spare to replace a disk — yes, you have to write the full disk. If you migrate a disk from a hot spare to an active disk, it’s already largely populated, so you only have to write the missing chunk. At least, that’s my limited understanding/reading. I’m not sure I fully grok what is happening as there aren’t necessarily dedicated spares in this setup. But I think the difference in your scenario is hot vs cold spares.