External Drive Light Flashing in Regular Pattern Continuously

If it's now stopped - and was just occasional and no significant disk activity, and didn't impede drive removal, and can't be identified, then best ignore it...

TraceyW said:

... my drives are no longer flashing ...

It was probably Microsoft Defender scanning the disks. It will do so again in the future.

Denis

Tracey,

TraceyW said:

Apart from this I've just tried scanning one of my external drives - and it won't do it!

Please may I check my understanding of this comment.
If you open File explorer & select ThisPC so that your drives are shown on the right-hand side, you should be able to right-click on any drive & select Scan with Microsoft Defender ...
Is that not happening?

TraceyW said:

Try3: You may have missed it but I did say that my husband's WD Elements drive (4TB) has been flashing in exactly the same way for over a year so if it was defender it would be constantly scanning the drive.

I have never worked out what the pattern of Microsoft Defender drive scans is.
- It may or may not remember when an external drive was last connected, and
- It may or may not remember what scanning it had previously conducted on that drive, and
- It may or may not wait for a period after connection, and
- It may or may not wait for an external drive to be temporarily idle, i.e. free of user-initiated activity,
- It may or may not wait for the CPU and/or other resources to be idle or below some unknown threshold level,
before deciding whether or not to scan.
My main backup drives had been in use for well over a year before it detected what it regarded as threats on one of them then, some time later, the same supposed threats on the other one.


All the best,
Denis

Perhaps use something like What's My Computer Doing?

Have a look at the site's Why is your harddisk working right now? page.

It's a very simple GUI.

Alternatively, use something like Lockhunter which will show you what processes have a drive open, hence the pulsing drive access LED.

Again, it's a very simple GUI.

Hope this helps...