Keeping my NAS drives connected

Welcome back shuanglong,

We appreciate the update! While we recognize that you may be the only user, along with having admin rights, we suggested that step with a newly created admin user will allow us to rule out any settings, features, apps, etc. that could be contributing to the behavior on your specific account.

For example, one setting that could cause this is found in Apple Menu > System Settings > Energy Saver > Put hard disks to sleep when possible. Is that setting enabled? If so, let's disable it to test to see if the same behavior occurs.

If so, we'd recommend disconnecting all external devices from your Mac. Ideally, it would be only the Mac (plus needed accessories such as mouse, keyboard, monitor) and single affected hard drive that are connected together.

Once complete, let's use the steps here to repair a storage device in Disk Utility: Repair a storage device in Disk Utility on Mac - Apple Support

Let us know the results.

Take care.

Good day to you shuanglong, 

Perhaps we can isolate the situation a bit. Are both drives formatted the same? If so, what are they formatted to? 

Do you notice the drive gets unmounted after specific steps or time frames? For example, after waking your Mac from sleep? 

Checking the situation in a new user may also tell us a bit more on what’s happening. Should you need assistance setting that up, the following article goes over how. It's always a good idea to test issues in an administrator user. Set up users, guests, and groups on Mac 

Thanks.

Are there differences in how the NAS storage is served, such as AFP or SMB?