cannot mount RAID drive(s) after Linux Mint 21 upgrade

[Mintstant Karma]

Yesterday I used the Upgrade Tool to upgrade my Linux Mint 20.3 installation to LM 21, as instructed here:
https://linuxmint-user-guide.readthedoc ... nt-21.html

Despite reading all the release notes and installation instructions I had questions, challenges, and/or mysteries at several points, and it was both the slowest and most complex Linux Mint update in memory. I think it was my first time using an "upgrade tool." Even though I followed the instructions carefully it was not always intuitive or clear what I should do next, and I began to wonder what the advantage was to that tool vs. a fresh install with the bootable flash drive I had made.

But I was curious, patient and methodical, taking numerous camera pictures along the way in case of trouble (thankfully) and it seemed it was ultimately successful. I arrived at a screen with a smiley face and the message "The upgrade was successful. Reboot the computer for all the changes to take effect." I did so.

After restarting, out of habit, I looked for the "2 TB drive" where most of my important daily files are -- but it was nowhere in the Computer directory/folder. However, I did see the two RAID components which comprise it...

Screenshot from 2022-10-05 00-40-55.png (5.36 KiB) Viewed 1969 times

I'm not able to mount either one (no surprise, since they depend on one another to make a whole drive).

By the way, all the icons in the Computer folder have that generic appearance, unlike in LM 20.3. Is that an indication of something important?

When I go to the LM menu and select a recently-opened file (which happens to reside on that unmountable drive) I get an error message saying VLC Media Player is unable to open the file. Well I should think not, because it's a TEXT file. I tried three other text files in the "recent" list, with the same result - VLC cannot open. Very strange. I tried right-clicking and opening with another application, but before I could even select the application I got a different error message. It came and went before I could get a screenshot or even fully read it, but again I'm not surprised I can't open it because I can't mount that drive!

Before the upgrade to LM 21, the RAID drive was easily mounted with a double-click on its (single) icon labeled "2 TB drive." After which I could open all those text- and other files. As it is now, I can't get to my most important daily files!

The only devices LM 21 lists in file manager Nemo are a flash drive and an external hard drive, both connected via USB. Unlike with LM 20.x, nothing internal is listed. Nevertheless, the internal SSD obviously self-mounts because all its contents are accessible in the "Home" directory. (So why doesn't it appear in the device list anymore?)

The biggest issue is the unmountable/unrecognized RAID drive.

As mentioned at the top, I have a bootable LM 21 flash drive, made for just such an emergency, and also a pre-upgrade Timeshift snapshot. But before I resort to either of those, I'd like to understand what happened... and hopefully also find a quicker fix to the non-mounting drive. I'm really kind of helpless without it. Thanks.

[Axel Larator]

mdadm up and running?
What does

cat /proc/mdstat

say?

[deck_luck]

How was your RAID originally setup? Did you use LVM RAID or dmraid/mdadm? You should check the Software Manger program to determine if the raid software exists or needs installing. It will be much quicker installing missing raid software than doing a TimeShift recovery.

[Mintstant Karma]

mdadm up and running?
What does

cat /proc/mdstat

say?

Hi Axel. After briefly educating myself about the "cat" command, here's what I got, but I don't know what it means...

mintstant@mintstant-MS-7522:~$ cat /proc/mdstat
Personalities :
unused devices: <none>

[Mintstant Karma]

How was your RAID originally setup? Did you use LVM RAID or dmraid/mdadm? You should check the Software Manger program to determine if the raid software exists or needs installing. It will be much quicker installing missing raid software than doing a TimeShift recovery.

Hi deck_luck. Evidently dmraid. I searched Software Manager for "raid" and this came up:

I confirmed by clicking on the Dmraid line and seeing the "Remove" button.

Edit: I searched Software Manager again for "lvm" and discovered I also have this installed:

[Mintstant Karma]

Can someone please help? I'm severely limited in what I can do until I can mount my drive again.

[deck_luck]

How did you originally setup the RAID0/1? Which commands did you use (mdadm)? Did you document the disk layout? If you are familiar with the terminal command line, please run and post the output from the following commands:

Code: Select all

sudo fdisk -l
sudo lsblk -f
cat -v /etc/fstab
grep -v '^#' /etc/mdadm/mdadm.conf
sudo mdadm --examine /dev/sd[a-z]*
sudo mdadm --detail --scan --verbose

[Mintstant Karma]

Sorry for the delay. I tried to post a reply several days ago and I'll spare you the details of why I couldn't, but they included a computer crash that wiped out the post before it was finished, a COVID booster, and other stuff I had to do.

In answer to your question about how I originally set up RAID, that's just it: I never did! When I bought the computer years ago it came with Windows 7 and RAID was already set up. Then I tried half a dozen Linux distros live, and most (but not all) recognized those two drives as RAID components without any setup on my part. It just worked. Finally, I installed Linux Mint, and it also recognized the RAID components without any input from me.

I've never had to set up anything to have RAID. That's what's so puzzling. It just suddenly stopped working with Linux Mint 21. Note: it didn't work from the Linux Mint 21 live session, either, which I thought was odd. But I guess I assumed the installed version would work as all previous ones have.

Also I just learned that RAID still works from one of the distros on an old bootable flash drive. The distro is Peppermint version 6, and I could easily mount the "2 TB" drive (1+1) and open files.

So apparently the drives are still fine and there's just some code missing in the new Linux Mint, at least in my installation. I've also seen people complaining about this with the Ubuntu version on which Linux Mint 21 is based, but I haven't fully explored the posts yet.

"Which commands did you use (mdadm)?"

I guess the answer is obvious now, from what I said previously. Also as mentioned in a previous post, mdadm doesn't appear to even be installed. (See screenshot above, of Software Manager.) Dmraid is apparently installed, but again I've never interacted with it.

Output from the commands:

Code: Select all

mintstant@mintstant-MS-7522:~$ sudo fdisk -l
[sudo] password for mintstant:         
Disk /dev/sda: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: Hitachi HDS72101
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x73f4ce26

Device     Boot Start        End    Sectors  Size Id Type
/dev/sda1  *     2048 3907037183 3907035136  1.8T  7 HPFS/NTFS/exFAT


Disk /dev/sdb: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: Hitachi HDS72101
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/sdc: 465.76 GiB, 500107862016 bytes, 976773168 sectors
Disk model: Samsung SSD 850 
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xe3a4af2d

Device     Boot   Start       End   Sectors   Size Id Type
/dev/sdc1  *       2048   1050623   1048576   512M  b W95 FAT32
/dev/sdc2       1052670 976771071 975718402 465.3G  5 Extended
/dev/sdc5       1052672 976771071 975718400 465.3G 83 Linux


Disk /dev/mapper/isw_ccejcdcbfb_Volume0: 1.82 TiB, 2000404348928 bytes, 3907039744 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 131072 bytes / 262144 bytes
Disklabel type: dos
Disk identifier: 0x73f4ce26

Device                                   Boot Start        End    Sectors  Size Id Type
/dev/mapper/isw_ccejcdcbfb_Volume0-part1 *     2048 3907037183 3907035136  1.8T  7 HPFS
GPT PMBR size mismatch (4294967294 != 35156656127) will be corrected by write.


Disk /dev/sdd: 16.37 TiB, 18000207937536 bytes, 35156656128 sectors
Disk model: d2 Professional 
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 8ED5940E-71C9-490F-9811-C7106A7C392C

Device      Start         End     Sectors  Size Type
/dev/sdd1      40      409639      409600  200M EFI System
/dev/sdd2  411648 35156654079 35156242432 16.4T Linux filesystem


Disk /dev/sdi: 115.63 GiB, 124151398400 bytes, 242483200 sectors
Disk model: USB Flash Drive 
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x20dd55ae

Device     Boot Start       End   Sectors   Size Id Type
/dev/sdi1        2048 242483199 242481152 115.6G 83 Linux
mintstant@mintstant-MS-7522:~$ 

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mintstant@mintstant-MS-7522:~$ sudo lsblk -f
NAME                     FSTYPE          FSVER  LABEL            UUID                                 FSAVAIL FSUSE% MOUNTPOINTS
sda                      isw_raid_member 1.0.00                                                                      
└─isw_ccejcdcbfb_Volume0                                                                                             
sdb                      isw_raid_member 1.0.00                                                                      
└─isw_ccejcdcbfb_Volume0                                                                                             
sdc                                                                                                                  
├─sdc1                   vfat            FAT32                   37A5-EC63                               511M     0% /boot/efi
├─sdc2                                                                                                               
└─sdc5                   ext4            1.0                     c35eb90f-bd2e-47db-9784-c02d3f654f22   49.8G    84% /
sdd                                                                                                                  
├─sdd1                   vfat            FAT32  EFI              67E3-17ED                                           
└─sdd2                   ext4            1.0                     7cb60077-1894-41d8-8554-850f6bdc061f   15.5T     0% /media/mintstant/7cb60077-1894-41d8-8554-850f6bdc061f1
sde                                                                                                                  
sdf                                                                                                                  
sdg                                                                                                                  
sdh                                                                                                                  
sdi                                                                                                                  
└─sdi1                   ext4            1.0    ADATA 124GB ext4 4f5d5658-b9ea-4cb7-b6c9-df20fd2a00cf    8.5G    87% /media/mintstant/ADATA 124GB ext41
sr0                                                                                                                  
mintstant@mintstant-MS-7522:~$ 

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mintstant@mintstant-MS-7522:~$ cat -v /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
# / was on /dev/sdc5 during installation
UUID=c35eb90f-bd2e-47db-9784-c02d3f654f22 /               ext4    errors=remount-ro 0       1
# /boot/efi was on /dev/sdc1 during installation
UUID=37A5-EC63  /boot/efi       vfat    umask=0077      0       1
/swapfile                                 none            swap    sw              0       0
mintstant@mintstant-MS-7522:~$ 

Code: Select all

mintstant@mintstant-MS-7522:~$ ^[[200~grep -v '^#' /etc/mdadm/mdadm.conf
grep: command not found
mintstant@mintstant-MS-7522:~$ ~

Code: Select all

mintstant@mintstant-MS-7522:~$ sudo mdadm --examine /dev/sd[a-z]*
sudo: mdadm: command not found
mintstant@mintstant-MS-7522:~$ sudo mdadm --detail --scan --verbose
sudo: mdadm: command not found
mintstant@mintstant-MS-7522:~$ 

No surprise on those last three commands.

[deck_luck]

...
Output from the commands:

Code: Select all

mintstant@mintstant-MS-7522:~$ sudo fdisk -l
[sudo] password for mintstant:       
Disk /dev/sda: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: Hitachi HDS72101
...
Disk /dev/sdb: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: Hitachi HDS72101
...
Device                                   Boot Start        End    Sectors  Size Id Type
/dev/mapper/isw_ccejcdcbfb_Volume0-part1 *     2048 3907037183 3907035136  1.8T  7 HPFS
...

Thank you for the details. Since it was previously used with Windows that explains why dmraid is active instead of the more common mdadm. Anyway, it looks like the ISW RAID set is active. For further information please post the output from the following command:

Code: Select all

sudo dmraid -s -s 

[Mintstant Karma]

Thank you for sticking with me.

Ah, interesting about Windows and dmraid. That makes sense.

I can't comment on "it looks like the ISW RAID set is active", though it's encouraging, because I'm not sure what that means or how you determined it. (I gather from a quick search that the 'I' is for Intel and 'S' is probably storage.) Maybe simply because the two hard drives are labeled "isw_raid_member." I was somewhat encouraged by that also, but my ignorance prevents me from being more so. :-/

I would agree that at least on a hardware or firmware level, RAID is working. Further evidence of that fact comes from this discovery in just the last couple of hours:

In addition to Peppermint (mentioned before), the RAID array is recognized, visible and self-mounting from live sessions of all of the following distros, each of which are at least a few years old...
Zorin
Linux Mint 17 Cinnamon
Linux Mint 19 Cinnamon

It is not recognized from Slacko Puppy 5.7 --- but as I recall it never was.

Those are just the leftover distros that still have any functionality, from four bootable flash drives I've created over the years.

Interesting to learn that mdadm is more common than dmraid, and I assume you mean in Linux circles. Perhaps that could be useful to me, and maybe that's where you were headed with your next instruction.

Here's the output:

Code: Select all

mintstant@mintstant-MS-7522:~$ sudo dmraid -s -s 
[sudo] password for mintstant:         
*** Group superset isw_ccejcdcbfb
--> Active Subset
name   : isw_ccejcdcbfb_Volume0
size   : 3907039744
stride : 256
type   : stripe
status : ok
subsets: 0
devs   : 2
spares : 0
mintstant@mintstant-MS-7522:~$ 

I hope that's useful to you, as it doesn't tell me a whole lot. It does, however, confirm my memory that it was a "striping" kind of RAID. (I was always worried that if anything went wrong with either component drive, I'd lose it all. Its only advantage was speed.)

I wonder if Linux Mint 21 (or Ubuntu 22.04) stopped supporting dmraid. I'm so curious about what has changed with this update to LM 21.

Looking forward to your reply. Thank you again.

[grndplane]

If I type in a terminal lsblk, I get>

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NAME    MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINTS
sda       8:0    0 465.8G  0 disk  
├─sda1    8:1    0   487M  0 part  /boot/efi
├─sda2    8:2    0 139.7G  0 part  /
└─sda3    8:3    0 325.6G  0 part  /home
sdb       8:16   0   3.6T  0 disk  
└─sdb1    8:17   0   3.6T  0 part  
  └─md0   9:0    0   3.6T  0 raid1 /mnt/md0
sdc       8:32   0   3.6T  0 disk  
└─sdc1    8:33   0   3.6T  0 part  
  └─md0   9:0    0   3.6T  0 raid1 /mnt/md0
sdd       8:48   0   3.6T  0 disk  
└─sdd1    8:49   0   3.6T  0 part  /media/MyBook
sr0      11:0    1  1024M  0 rom   
sr1      11:1    1  1024M  0 rom   

I use MDADM software raid type 1. You can see the two drives sdb and sdc that make up md0 raid.
Then if I type in a terminal sudo blkid, and type my password. I get >
/dev/md0: UUID="02dfd47a-a3d8-40de-8f63-cbeebcedb653" BLOCK_SIZE="4096" TYPE="ext4"

and finally I add lines to my /etc/fstab that look like >

# Raid1 Array
UUID=02dfd47a-a3d8-40de-8f63-cbeebcedb653 /mnt/md0 ext4 users,defaults 0 0

too match the UUID I found with sudo blkid.

Hope this helps.

[deck_luck]

Code: Select all

mintstant@mintstant-MS-7522:~$ sudo dmraid -s -s 
[sudo] password for mintstant:         
*** Group superset isw_ccejcdcbfb
--> Active Subset
name   : isw_ccejcdcbfb_Volume0
size   : 3907039744
stride : 256
type   : stripe
status : ok
subsets: 0
devs   : 2
spares : 0
mintstant@mintstant-MS-7522:~$ 

The dmraid -s -s command proves LM21 is using dmraid. We can try to manually mount the device as a test. From the Linux Mint Menu search for Disks click the Disks utility. Find the isw_ccejcdcbfb_Volume0 device in the left Devices column and click it. The right side will populate with the isw_ccejcdcbfb_Volume0 details. Select the part1 (partition1) and click mount button. The mount button looks like a media player start button or a bold right arrow.

Please do not follow bad advice of attempting to use mdadm on an existing dmraid. Geez Louise.

[Mintstant Karma]

I use MDADM software raid type 1. You can see the two drives sdb and sdc that make up md0 raid.
Then if I type in a terminal sudo blkid, and type my password. I get >
/dev/md0: UUID="02dfd47a-a3d8-40de-8f63-cbeebcedb653" BLOCK_SIZE="4096" TYPE="ext4"

and finally I add lines to my /etc/fstab that look like >

# Raid1 Array
UUID=02dfd47a-a3d8-40de-8f63-cbeebcedb653 /mnt/md0 ext4 users,defaults 0 0

too match the UUID I found with sudo blkid.

Hope this helps.

Thanks for the input, but I don't know how I can use this information, at least for now. I'd rather focus on the software I already have installed, which worked for years until Linux Mint 21 was installed. Since I didn't have to do anything to set up RAID before, the question for me is what changed during the installation, and whether I can revert that change. If that approach fails I may resort to MDADM, and then maybe something you've shown me will click. Until then, making more changes would seem to only complicate things.

[Mintstant Karma]

The dmraid -s -s command proves LM21 is using dmraid. We can try to manually mount the device as a test. From the Linux Mint Menu search for Disks click the Disks utility. Find the isw_ccejcdcbfb_Volume0 device in the left Devices column and click it. The right side will populate with the isw_ccejcdcbfb_Volume0 details. Select the part1 (partition1) and click mount button. The mount button looks like a media player start button or a bold right arrow.

Please do not follow bad advice of attempting to use mdadm on an existing dmraid. Geez Louise.

I'm pretty familiar with the Disks utility and had already opened it to look at these RAID devices. Nothing useful was revealed to me, although it was interesting to see that each device appears and so does the 2 TB "block" device -- the combination I need to access. Note: there's no indication which is the isw_ccejcdcbfb_Volume0 device, but I know from experience which devices are the RAID members, and I looked at both of them.

None of them are mountable from anything I can see. I know the "play" icon you're describing and it's not there on either of the 1 TB RAID member devices nor on the 2 TB array/drive. No surprise since I had also tried to mount the 1 TB devices from within Nemo, and each said it could not be mounted. Also as mentioned early-on, I'm not surprised by that either, since each one depends on the other. Neither is a whole set of useful data, just one stripe in the candy cane or barber pole that is the useful, complete drive.

Here's what I see for each of the RAID devices.

This is getting increasingly disturbing. The ability to read a RAID drive must surely exist in this version of Linux Mint and Ubuntu or I would certainly think it would have been a "known issue." This is not something minor like fonts not showing up correctly; this is accessing my data!!

I really appreciate your time, but it's upsetting that I'm not seeing more discussion of this critically important problem. Can I really be one of the very few going through it? Maybe RAID drives are rare on home computers. It's hard to believe something this fundamental depends on help from a kind forum member!

[Mintstant Karma]

mdadm up and running?
What does

cat /proc/mdstat

say?

Hi Axel. After briefly educating myself about the "cat" command, here's what I got, but I don't know what it means...

mintstant@mintstant-MS-7522:~$ cat /proc/mdstat
Personalities :
unused devices: <none>

Re-reading this thread I just realized you asked me about mdadm, too, and I didn't reply. No, that software is not installed. Evidently, my computer is using software called dmraid instead. But as you can see if you read more of this thread, that seems to be working as it has for years with multiple versions of Linux --- until upgrading to Linux Mint 21.

[deck_luck]

If you want me to help please stay focused on my replies instead of wondering off course with other forum member's replies.

Let us attempt to manually mount the raid set. Please post the output from the following commands:

Code: Select all

sudo df -Thxtmpfs
sudo mkdir /mnt/raid_set
sudo chmod 755 /mnt/raid_set
sudo mount /dev/dm-0 /mnt/raid_set
sudo df -Thxtmpfs

...
This is getting increasingly disturbing. The ability to read a RAID drive must surely exist in this version of Linux Mint and Ubuntu or I would certainly think it would have been a "known issue." This is not something minor like fonts not showing up correctly; this is accessing my data!!

I really appreciate your time, but it's upsetting that I'm not seeing more discussion of this critically important problem. Can I really be one of the very few going through it? Maybe RAID drives are rare on home computers. It's hard to believe something this fundamental depends on help from a kind forum member!

The ISW is an old technology and it was commonly used in the Microsoft Windows world. The Linux kernel provides support for it to allow interoperability and or dual booting Windows/Linux using the same raid set. On a modern Linux only installation it would be an extremely rare case to find dmraid using an ISW raid set.

[Jo-con-Ël]

It looks like there are problems with fake/hardware RAID on new Mint edition/kernel. I have tried lot of things but the only way to access RAID sub-volumes/partitions was this workaround.

If doing as deck_luck proposed on last post fails, you can try running

Code: Select all

sudo kpartx -a /dev/mapper/isw_ccejcdcbfb_Volume0

Then run Disks and choose/select that 2TB Block Device (/dev/dm-0) on the left to see and mount partition (/dev/mapper/isw_ccejcdcbfb_Volume0-part1) on the right

and/or find volume/partition on file browser Devices bookmarks and try to mount it.

About Computer contents, you will never be able to mount those Hitachi disks as you have not direct access to disks forming RAID, but now you will find that subvolume/partition on RAID with different icon and mount it also from there with double-click (or right-click to mount/unmount).

[Mintstant Karma]

If you want me to help please stay focused on my replies instead of wondering off course with other forum member's replies.

You seem to be suggesting that I did wander off-course. I'll try not to take offense at that implication since I'm not sure, but for the record I've been highly focused on your replies, and practically said as much to 'grndplane': "I'd rather focus on the software I already have installed... Until then, making more changes would seem to only complicate things."

I understand where you're coming from. I agree with the idiom "too many cooks spoil the soup." But I took no action on anything suggested in the two previous posts; I was merely being polite and responding to those people for trying to help -- and that's not going to stop. I value your IT background, and if someone else were to suggest something that does sound reasonable, I would see what you thought before trying it. OK? Please trust my focus as I've trusted your advice.

Now then: I have to run to the store in a few minutes so I can't yet try your latest suggestion, but I look forward to doing so after I get back. Thanks.

[Mintstant Karma]

Let us attempt to manually mount the raid set. Please post the output from the following commands:

Code: Select all

sudo df -Thxtmpfs
sudo mkdir /mnt/raid_set
sudo chmod 755 /mnt/raid_set
sudo mount /dev/dm-0 /mnt/raid_set
sudo df -Thxtmpfs

OK. Here they are:

Code: Select all

mintstant@mintstant-MS-7522:~$ sudo df -Thxtmpfs
[sudo] password for mintstant:         
Filesystem     Type  Size  Used Avail Use% Mounted on
/dev/sdc5      ext4  457G  384G   51G  89% /
/dev/sdc1      vfat  511M   20K  511M   1% /boot/efi
/dev/sde1      vfat   58G  5.9G   52G  11% /media/mintstant/MULTIBOOT
/dev/sdd2      ext4   17T  2.3G   16T   1% /media/mintstant/7cb60077-1894-41d8-8554-850f6bdc061f1
/dev/sdj1      ext4  114G   99G  8.6G  93% /media/mintstant/ADATA 124GB ext41
mintstant@mintstant-MS-7522:~$ sudo mkdir /mnt/raid_set
mintstant@mintstant-MS-7522:~$ sudo chmod 755 /mnt/raid_set
mintstant@mintstant-MS-7522:~$ sudo mount /dev/dm-0 /mnt/raid_set
mount: /mnt/raid_set: special device /dev/dm-0 does not exist.
mintstant@mintstant-MS-7522:~$ sudo df -Thxtmpfs
Filesystem     Type  Size  Used Avail Use% Mounted on
/dev/sdc5      ext4  457G  385G   50G  89% /
/dev/sdc1      vfat  511M   20K  511M   1% /boot/efi
/dev/sde1      vfat   58G  5.9G   52G  11% /media/mintstant/MULTIBOOT
/dev/sdd2      ext4   17T  2.3G   16T   1% /media/mintstant/7cb60077-1894-41d8-8554-850f6bdc061f1
/dev/sdj1      ext4  114G   99G  8.6G  93% /media/mintstant/ADATA 124GB ext41
mintstant@mintstant-MS-7522:~$ 

Once it has served its purpose, please let me know if I need to keep that new directory, and if not, how to delete it. A moment's research suggests rm or rmdir followed by "/mnt/raid_set", but I'd rather see it from you. I realize from experience going all the way back to MS DOS that the directory may be insignificant in terms of functionality and disk space, but I'm still relatively green with Linux terminal commands so I'm careful about running them except for the very few I've already learned. In fact I briefly research each new one first. No doubt your IT background makes you a lot more trustworthy than many others who post on these forums, but I'm ultimately responsible for my computer, and I've been more or less abandoned in the past by one or two users after getting myself into a mess. (I'm also taking Timeshift snapshots.)

Likewise, is there anything I need to reverse after running sudo chmod 755 /mnt/raid_set? No rush; I can wait till you are finished with your suggestions.

[Mintstant Karma]

...
The ability to read a RAID drive must surely exist in this version of Linux Mint and Ubuntu or I would certainly think it would have been a "known issue."
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I really appreciate your time, but it's upsetting that I'm not seeing more discussion of this critically important problem. Can I really be one of the very few going through it? It's hard to believe something this fundamental depends on help from a kind forum member!

The ISW is an old technology and it was commonly used in the Microsoft Windows world. The Linux kernel provides support for it to allow interoperability and or dual booting Windows/Linux using the same raid set. On a modern Linux only installation it would be an extremely rare case to find dmraid using an ISW raid set.

Does it, though? (responding to the blue text)
That seems to be the question, as of Ubuntu 22.04 / Linux Mint 21. That's not sarcasm; I'm really wondering based on the evidence. And ok, I get that ISW is old, and its use with dmraid is rare. Fair enough. I guess your point is that it's so rare that if they pulled support for ISW / dmraid, a pre-installation notice/warning wouldn't be worth mentioning, or might not even cross their minds. {sigh} It wouldn't be the first time I've thought I might be better off with a new machine.

But if support has been pulled, I would still like to know so I understand what happened, and can happily go back to LM 20.3 knowing I tried.

No reply to this section is needed, deck_luck. I'm just venting, and hoping someone in power will ultimately see these comments. For now I'm still willing to pursue any further steps or new suggestions you may have.