I run Western Digital WD Red Pro drives in my FreeNAS box. They’re 7200 RPM, SATA 6 Gb/s, CMR drives, and they’ve been fast and reliable in that role.

The one thing to watch for: some NAS drives ship as SMR, not CMR. SMR drives overlap their tracks to pack in more capacity, which tanks write performance and can cause problems rebuilding a ZFS array. Always check the exact model number before you buy and confirm it’s CMR.