by rottegift » Tue Jun 28, 2016 10:03 am
It's treated as metadata and additionally you can cause extra ditto copies with "zpool dedupditto=number" where number is >= 100 or is zero (the default); when the reference count for a table entry goes above number when number is nonzero, the (many-entry) record it's in will be ditto-copied (see zio_ddt_write() for details).
Don't do deduplication on ANY pool where ANY device in the pool has a nonzero seek time. You'll be sorry eventually.