Situation: WD Easystore 8TB USB 3 HDD are not recognized by the PR4100 when plugged in to the rear ports. When PR4100 is powered down and then the WD Easystore HDD are plugged in to the rear ports they are recognized. However, the USB drives will randomly disconnect from the PR4100. There are two WD Easystore 8TB USB drives and they are both formatted as MacOS (HFS+).
Troubleshooting: Both WD Easystore USB drives check as OK using WD Drive Utilities. Both drives have the sleep timer turned off using WD Drive Utilities. Both drives work with no problems and no disconnects when attached to a computer such as a Mac. WD Support suggests RMA an Easystore USB drive an then suggests RMA the PR4100.
Research in WD Online Forums confirms that this issue is common with My Cloud devices. Suggestion was that reformatting the USB drive having the problem would typically solve the issue. Both Easystore 8TB USB drives were reformatted as MacOS (HFS+). Drives were then attached to the PR4100. Result is the same They are recognized without the power down of the PR4100 being required however they each randomly disconnect from the PR4100.
One of the WD Easystore 8TB USB drives was reformatted as NTFS using NTFS for Mac by Paragon. This drive was then reconnected to the PR4100. The drive was recognized upon being plugged in to the PR4100. After three hours the drive had not disconnected. The second WD Easystore 8TB USB drive was reformatted as NTFS. The second drive was reconnected to the PR4100 and was recognized by the PR4100 upon being plugged in. After 12 hours neither drive has disconnected from the PR4100.
It would appear that although the PR4100 is supposed to support MacOS formatted external drives, it does not do so.
An additional issue was noted. With the two WD Easystore 8TB USB drives attached and online the dashboard of the PR4100 reports the correct total free space but it classifies al files as Other. This condition remains even after both USB drives are ejected from the PR4100.
In addition the PR4100 has been assigned a fixed IP address on the network but will randomly disappear from the network. Will not be accessible from the Finder of my iMac and will not be accessible through My Cloud although the dashboard can still be accessed. Rebooting the iMac solves the problem until it reoccurs.
Solution: It appears that external HDD must be formatted as NTFS to consistently work with the PR4100 and to not randomly disconnect from the PR4100.