A disk never goes to sleep during an active transfer.

Old disks did a temperature calibrary regularly - even when busy handling transfers - which was a reason why video editing systems had to buy special disks with firmware that did progressive t-cal operations instead of doing a full calibration now and then.

But a 30s freeze in the middle of a transfer should not be caused by any power-save feature. The Explorer may freeze from this, since it may touch a number of disks when refreshing the displayed information. But normal programs do not access any disks but the ones where it are accessing data - and these disks will then stay awake.