My NAS has two HDDs configured in RAID1. I recently started to use Qcenter to monitor the NAS a bit more closely, and I noticed something that was puzzling. The IOPS of the one HDD sometimes diverges quite a bit from the IOPS of the other, and so does the latency. I can understand the latency difference, because that HDD (HDD2) is a (new) WD Red while the HDD1 is an (old) WD Gold. But: why would the IOPS differ so dramatically when the disks are in RAID1?
This is a chart of the IOPS:
…and this is a chart of the latency:
HDD1=WD Gold 8TB (WD8003FRYZ), 2,600 power on days
HDD2=WD Red Plus 8TB (WD80EFPX), 270 power on days