Raid 1 rebuild 17% after 5 days?

Hi! My NAS seems to lose power at last wednesday. I dont know, because i was on a journey. Now it is rebuilding disks. But is it right, that the rebuild takes that long? There are 2 8TB disks inside and the rebuild reached up to 17%. For me, that seems to be a bit slowly?

Any ideas?

See if this article helps - https://support-en.wd.com/app/answers/detail/a_id/25493/kw/RAID%20rebuild