Raid 5 creation because long time for synchronization

[DMD61]

Good morning.
My system consists of TS-431K + TL-D800C, I am creating Raid 5 pool for the first time on the expansion unit, synchronization has been triggered which results about 21hours.
I don't understand why all this time, when I did the first Raid 5 pool on the nas (TS-431K) it was very fast.
The only doubt I have, is that in the NAS (TS-431K) I put all new and unformatted HDDs, in the expansion unit (TL-D800C) I put disks used on pc's that I formatted (unallocated) with Windows and then put them in the expansion unit.
Can this be the problem possibly what do you recommend?
Thank you very much

[FSC830]

No, not really.
But formatting used disks it not mandatory, removing all partitions instead is sufficient.

Actually I am wondering about a fast raid5 pool sync at NAS.
At all of my NAS creating a raid group or pool (depends to model/QTS version) the snychronizaion tooks every time about several hours.
At my 6 and 8 bay NAS (3 TB disks) the sync lasts about 15-20 hours - as far as I remember.
So 21 hours seems to be in time range I experienced.

Regards

[DMD61]

What I don't understand because in the main unit (TS-431K) the time taken was a few hours with 4 new 4TBHDDs.
In the expansion unit that supports 8HDDs I only put in 5HDDs of 4TB.
Thanks