What are these DM devices?

Question

On a CentOS 5 server:

fdisk -l 2>/dev/null

shows many /dev-dm-XX disks.

• /proc/mdstat is empty, so they are not software RAIDs
• ps -ef | grep -i multipath | grep -v grep and multipath -ll shows NOTHING! So they are not disks from multipath.
• all have an old "last modification timestamp: 1 year ago
• strings $(/dev/dm-16 | head) for example, shows that there are/were (?) data on them!
• mount | grep dm gives nothing
• pvs | grep dm gives nothing

Question: what are these dm- disks?

The LVM Volume Group for the OS uses a local disk, that's ok, we are searching that what are these "dm-*" disks :)

Answer 1

How do you think you are mounting your filesystem(s)?

$ findmnt /
TARGET SOURCE                            FSTYPE OPTIONS
/      /dev/mapper/alan_dell_2016-fedora ext4   rw,relatime,seclabel,data=ordered

$ ls -l /dev/mapper/alan_dell_2016-fedora
lrwxrwxrwx. 1 root root 7 Mar 14 09:53 /dev/mapper/alan_dell_2016-fedora
-> ../dm-0

$ ls -l /dev/dm-0
brw-rw----. 1 root disk 253, 0 Mar 14 09:53 /dev/dm-0

$ lsblk
NAME                      MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda                         8:0    0 465.8G  0 disk 
├─sda4                      8:4    0   450M  0 part 
├─sda2                      8:2    0   128M  0 part 
├─sda7                      8:7    0 371.4G  0 part 
│ └─alan_dell_2016-fedora 253:0    0    40G  0 lvm  /

$ cat /sys/class/block/dm-0/dm/name
alan_dell_2016-fedora

$ sudo dmsetup table
alan_dell_2016-fedora: 0 83886080 linear 8:7 2048

P.S. I also tried running your fdisk -l command on my newer OS (Fedora Linux 30). Instead of showing the /dev/dm-* devices, it shows me the names of all the /dev/mapper/* links.