External drives showing uo twice in Finder sidebar

Just restart your iMac, it must be a temporary glitch

macOS sometimes shows duplicate entries for mounted drives when the Finder’s sidebar cache or the com.apple.sidebarlists preference is enabled.plist file gets corrupted, especially with multiple partitions or identical drive names.

Try this: eject all external drives, go to ~/Library/Preferences/, and delete com.apple.sidebarlists.plist. Then restart Finder (Option + right-click Finder in Dock > Relaunch) and reconnect your drives one by one.

It usually cleans up the duplicates. If not, it’s just a cosmetic bug, your data’s safe, but Apple does need to fix it properly.

Peter Black 2 wrote:

Thanks bit It's not a temporary glitch - actually it happens every time the iMac goes to sleep and then wakes up again.

It sounds like the external drive is losing its connection during sleep, so macOS creates a new mount point for the external volume when the system wakes up.

See if you can disable "Put hard disks to sleep when possible"....this option may only appear when an external drive is connected to the computer with more recent versions of macOS. This option may be located in the Battery System Settings......Click the Options button (at least on Ventura....Apple has been moving settings around a lot these past few years).

This can happen when the external drive uses bus power to power the drive. Try using a dedicated power adapter for your external drive, or connect the external drive to a powered USB3 hub or dock.

If this is an M-series laptop, then you may want to change the "Allow accessories to connect" Privacy & Security Settings to "Always" to see if that makes a difference.

FYI, not all external drives can handle sleep mode properly.

You may also have an issue involving third party software that may be contributing to the problem as well.

Edit: You have also neglected to provide specific details such as the exact model of your Mac, version of macOS, as well as the exact model of this new external drive including how it is connected to the computer. The type of file system used as well as whether you are using the manufacturer's proprietary software to manage this problematic external drive. These are all essential things needed for troubleshooting the issue.

Writing an effective Apple Support Communities Question - Apple Community

Peter Black 2 wrote:

(however this has been happening to people for at least 5 years so I expect this would be independent of macOS version)

Irrelevant. From reading thousands of posts on this forum for years now, many of the users never provide enough details, nor do they properly troubleshoot the problem even when we offer suggestions (assuming they follow our instructions exactly....many do not follow them properly). There are just too many unknowns & too many unknown combinations of hardware & software to make any conclusions.

Apple has tightened up the communication between external devices with the last several versions of macOS where a better quality higher end cables are needed. This is especially important for connections to external displays and external drives. Many people have solved their drive issues with a new high quality cable. The cables which the manufacturers provide are usually just barely able to work (fine if they do, but everyone should have at least one good high quality cable handle for troubleshooting).

I'm reluctant to buy a powered hub because of this.

In my own personal experience plus reading a few posts on this forum, sometimes external drives just work more reliably when connected to a good quality hub (may as well be powered as well to eliminate power related issues as well...may not always need to use that hubs power adapter, but it helps with troubleshooting).

The exact model of drive is difficult since I have 2 new ones and I'm not sure which MIGHT have been the culprit. One was a Sandisk and the other was a Samsung.

You must determine which drive or perhaps which other connected device may be causing the problem. It is best to disconnect all external devices & concentrate on testing one device at a time all by itself just so other devices do not interfere.

While writing this reply I just thought of a possible reason.....when powering on a drive...that may require a surge of power...if you have multiple devices connected, then the surge of needed power to each device may cause issues & some device(s) may suffer from it.

Plus as I mentioned previously....some SSDs don't always wake up properly from sleep.

The drives are all formatted APFS.

Good. I know people have reported issues with exFAT ever since Apple rewrote the FAT/exFAT driver several years ago.

I'm not using the proprietary software although I did download them. I will look at the "sleep when possible in system preferences." Does anyone know where the plist is actually located - that would help too. Many thanks.

No idea, just easier to locate the setting within System Settings. Unfortunately since it resides deeper with in the settings I could not locate it by using the search feature in System Settings (why Apple?).

Apple is not here on this forum. We are just other regular users such as yourself. If you want tell Apple about the issue, then provide feedback here:

Feedback - macOS - Apple

If you want Apple to assist you, then click the Support link & create a case with Apple Support.

If you want assistance from regular users on this forum, then how about providing a screenshot showing the issue.

Peter Black 2 wrote:

There was a previous thread regarding this in 2023 - apparently Apple hasn't addressed this (like so many other things they are consumed with making new shiny toys and not fixing the ones that have been around a long time). There have been other similar threads which have been closed. Please stop closing these repeating threads and fix the problem.

This issue began a month or two ago. It may have coincided with adding a new external HD but i'm not sure. APPLE ITS NOT UP TO US TO TROUBLESHOOT YOUR BUGS! PLEASE FIX! I have two 8TB drives, a 5TB drive, a 3TB drive that is partitioned and a 4TB drive that is also partitioned running on a 2020 Intel iMac.

It's difficult for Apple or anyone to troubleshoot an issue without complete information. I have 7 SSDs (two of which have 5 partitions each), some of them with individual encrypted disk images on them, and all of the mounted volumes show properly as a single entry in the Finder sidebar both on Sequoia and now on Tahoe.

As for threads being closed, that is time-dependent and automatic. Some threads are closed with no resolution because, in many cases, the OP never returns to the thread to provide relevant information needed to help.