Off topic, but: I purchased three refurb 6TB HGST He HDDs in Jan. from a reputable shop. All three failed last month. I was so happy that the shop completely refunded all of them because the warranty is generally very limited on refurb HDDs. Normal RMA is 5yr on this specific model.
There's no way refurb drives are cost effective for these environments.
That all three drives lasted this long then failed within a month is very suspect. This sounds less like random failure indicative of the quality of refurbished drives in general, and more like a defect common to all three drives.
Because of such plagues, data-centre operators often mix drives of different manufacturers, models, batches and ages. Running heterogeneous devices in a redundant array helps makes the failure distribution more random so that the safety margin is less likely to be suddenly overwhelmed by correlated failures.
Beyond a functional test, checking the SMART data for an indication of overall drive state and He containment, and then giving the drive a quick clean, it would be interesting to know the supplier's scope for 'refurbishing' an He drive.
There's no way refurb drives are cost effective for these environments.