Mac Mini shows Multiple HDD HTS and Data Volumes - How Do I correct?

That hard drive is in really bad shape with over 8,600 sectors pending reallocation.....that is extremely bad.

Do you have a backup? I sure hope so. If not, then do not do anything else with this drive. Power it off immediately so the failure does not get any worse. Send the drive to a professional data recovery service to see if they can recover any of your data. Drive Savers can provide free estimates and is recommended by Apple and other OEMs.....just make sure to tell them that the SMART report shows 2,000 reallocated sectors with the "Current Pending Sectors" showing 8,600.

FYI, I have successfully recovered data from hundreds of hard drives over the years so I do have some experience here. I am not a professional, but consider myself an advance amateur data recovery person who only used a free open source utility on Linux to clone the drive at a low level so that errors could be easily skipped. With 8,600+ sectors pending reallocation, there is no way macOS or any other utility will be able to recover any data due to the errors which will be encountered.....macOS and those utilities are unable to deal with those errors and will keep trying to read the drive which will make the failure worse.

Due to the number of pending sectors awaiting reallocation, I'm not sure if using an external USB macOS external boot drive will be an option since the internal hard drive failure may affect the performance of the external USB SSD. You may need to actually replace the internal hard drive with an SSD.

OK, the fundamental reasons your Mac Mini seems to run slowly are that you have only 8GB RAM and you have a slow (5400rpm) hard drive.

While Monterey (macOS 12) will run in 8GB RAM, that's the bare minimum required.

5400 rpm hard drives were always considered to be slow but their performance could be acceptable for light use, at least in the HFS+ days (pre-Catalina). APFS however is optimized for SSDs, not hard drives, and HDD performance can be very bad under APFS.

Please do 1 more thing. Open Terminal and type this command:

diskutil list

Post a copy of the results. It will give us a bit more visibility into the organization of your drive(s).

It would help to post the complete DriveDx text report so we can check the health of the hard drive. The hard drive is the most likely culprit even though the EtreCheck report showed the hard drive had speeds of 70MB/s which is good, but there still may be some bad sectors on it.

The multiple APFS volumes is not the cause of the performance issues. No need to deal with the extra APFS volume yet since you have more than enough Free space on your drive.

Others who know more about Monterey & APFS disk structure may be able to tell you much more & better information about what is going on here.

However, based on my limited experience, things just don't look right. DriveDX is telling you that the HDD is beginning to fail. In my book that's a show stopper. Second, I'm scratching my head about why the macOS snapshot (a necessary component, the SSV that your Mac boots from) resides in the Data volume. It should be in the Apple HDD HTS volume. Maybe you inadvertently installed macOS in the Data volume, as BDAqua suggested, but I can't tell.

If it were me, I'd back up all data, replace the HDD with an SSD and reinstall Monterey from scratch. While the HDD can be replaced, it unfortunately involves a complete teardown. You can view the process on iFixit.

Pls. give us a slightly different screenshot. Go back in to Disk Utility, do View > Show All Devices and then do another screenshot. It will give us a better view of your entire disk.

The snapshot is probably a consequence of running Time Machine. TM does do snapshots. Do you have TM enabled?

The Apple HDD HTS - Data - Data volume may possibly be from an upgrade that wasn't complete.

The slowness you reported is probably not due to having multiple volumes even if they seem to have the same name. Tell us more about your Mac Mini. Exactly what model, RAM, any history of upgrades.

It would also help if you run Etrecheck and post a copy of its report here. It was written by a member of these forums to help diagnose problems. It is safe to use and does not report any personal information; just info about your Mac.

My recollection is that Volumes with "Data - Data" in their name are a result from either multiple macOS upgrades or a failed upgrade that was later redone. Did either of these situations happen in your case?

Do both of these volumes show up on your Desktop? (Make sure Finder preferences has "Hard disks" checked).

Also, in DU, select each of these volumes one at a time and tell us what it says for Device in the table details for each:

• Apple HDD HTS - Data
• Apple HDD HTS - Data - Data

That is normal.

As MartinR has stated, it's a slow machine for today's OSes, but...

Try one of these two…

You can use Drive DX to possibly get a better view of Drive health…

https://binaryfruit.com/drivedx

Thanks to Jack-19…

It may be wise to run SMART Utility to check the drives' health. 

It will only help confirm suspicions or not.

The

• Apple HDD HTS - Data - Data

means you likely installed the OS to the Data Partition that already existed.

The existence of the startup snapshot in the volume named Data-Data is what has been puzzling me. Your explanation makes sense.