This is actually a fairly complicated topic.
Let's start by talking about how normal standby works without the StableBit Scanner getting involved.
Windows "Put the Disk to Sleep" Feature
Normally, Windows will monitor the disk for activity and if there is no disk activity for some preset amount of time it will put the disk to "sleep" by flushing all of the data in the cache to the disk and sending a special standby command to it. At the same time, it will remember that the disk is asleep in case any other application asks.
Shortly after the disk goes to sleep, the StableBit Scanner will indicate the fact that the disk is asleep in the Power column. Normally, the Scanner gets the power status of the disk by querying Windows and not the disk.
It does not query the disk directly for the power state because Windows considers this power query disk activity and wakes up the disk as a result.
Now, things get a bit more complicated if you want to include the on-disk power management in this picture.
Disks can optionally support these features, which can put them to sleep without Windows knowing it:
- Advanced power management.
- Standby timer
Advanced Power Management
This is a technology that implements power consumption profiles. For instance, if you don't care about performance but want maximum power savings, then you can tell your disk just that. Simply set the Advanced Power Management to Minimum Power Consumption. Or you can do the exact opposite by setting it to Maximum Performance (which guarantees no standby).
With Advanced Power Management you don't concern yourself with "sleep timeouts", like in Windows. You simply state your intent and the disk will adjust various parameters, including the standby time, according to your setting.
The implementation of Advanced Power Management is completely up to the manufacturer of the drive, and there are no specifications that explicitly state what each power mode does. This entire feature may not even be supported, depending on the disk model.
The Standby timer is more widely supported because it is an older feature. You simply specify after how much disk inactivity you would like the disk to be put to sleep. This is similar to how things work in Windows, except that the low power mode will be initiated by the disk firmware itself.
Again, the implementation of this is up to the manufacturer of the drive.
StableBit Scanner "Put into Standby"
In the StableBit Scanner, you can right click on a disk and put it into standby mode. What this does is send a power down command to the disk. This type of power down is equivalent to what Advanced Power Management or the Standby Timer would do.
More importantly, when a disk is powered down in this way, Windows will not be aware that the disk is in a low power state, and will continue to report that the disk is still powered up. This is not an issue because the disk will simply spin up the next time that Windows tries to access it.
But this leaves the StableBit Scanner with a dilemma. If we can't query the disk for the power state directly, how do we report the true power state of the disk? What the StableBit Scanner implements is a power state in which it's not sure whether the disk is in standby or active, and this is what you were seeing.
Forcing the StableBit Scanner to Query the Power Mode from the Disk
If you want to use on-disk power management exclusively, and you don't care about Windows putting your disks to sleep, you can instruct the StableBit Scanner to query the power mode directly from the disk.
When this is enabled, you will no longer see the standby or active message, but Windows will never try to put that disk to sleep. That's why this is off by default.
And just to make things even more complicated, sometimes a disk will wake up when it's queried for SMART data.
To this end the StableBit Scanner implements some more settings to deal with this:
I hope that this clears things up.