Is it normal for hard disk spin up and spin down frequently?

I have a new 4TB WD My Book Studio (with metal casing) permanently attached to an iMac 2013 as Time Machine backup. It seems to work well except I am puzzled by the behavior of the HDD in regard to switching between  idle, standby and activity  modes. For example, the HDD often spins down and goes into standby mode (indicator light slowly flashing) and only a few seconds later spins back up and goes into idle mode (indicator light steady on). Intuitively I would think frequent HDD spin up and spin down would increase wear and tear on the HDD as well as electricity consumption, am I correct? Why is it necessary to spin down the HDD completely while the computer is being used? I have asked WD tech support this question, but they only gave boilerplate answers, never specifically addressing my concerns. Thanks in advance to anyone who can explain this to me.


As long as the hard drive is not being used it will stay in stand by mode. Check if you have any software that might be waking up the hard drive.