Audits and egress repair do reads mostly, the write operations are happened on databases, bandiwdth.db in particular, to store how many bytes were transferred (because it’s a paid traffic).
However, SMR disks are known as incredible slow, this is why it’s not recommended to use them for storagenode - there are a lot of small write and read operations, which is suboptimal for SMR.
There is no good solution for SMR disks, except running several nodes in the same network (each on own HDD) to spread the load, and move databases to the other disk - preferable on SSD.