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Are there any other (de)merits about the following FS mounting methods?

For example:

  1. the DM method, just means /dev/mapper/<VG>-<LV>, can handle its own multipath I/O.
  2. the non-DM methods, such as UUID/LABEL/LVM, cannot handle their own multipath I/O?
    1. UUID: the system randomly generated persistent logical ID, without its original low-level attributs
    2. LABEL: the user customarily defined persistent logical ID, without its original high-level attributs
    3. LVM: also means /dev/<VG>/<LV>, versus /dev/mapper/<VG>-<LV>, it almost has no any (de)merit?
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I'm not really sure I fully understand your question, but there's no difference between mounting /dev/mapper/vg-vl, /dev/vg/lv and /dev/disk-by-[uuid|id|partlabel]/, these are simply symlinks to the /dev/dm-<number> device mapper block device nodes created by kernel. These symlinks are created by UDev rules and are there simply for convenience and ease of use.

$ ls -la /dev/disk/by-uuid/*
lrwxrwxrwx. 1 root root 10 Feb 26 06:57 /dev/disk/by-uuid/122d1e25-4e4b-4ac4-b1b5-33d5e942f815 -> ../../dm-1
...
$ ls -la /dev/mapper/*
lrwxrwxrwx. 1 root root       7 Feb 26 06:57 /dev/mapper/fedora-root -> ../dm-1
...
$ ls -la /dev/fedora/*
lrwxrwxrwx.  1 root root    7 Feb 26 06:57 root -> ../dm-1
...

Multipath has nothing to do with this, if you are using DM multipath, you'll have the "extra" /dev/mpathX devnodes on top of the disks and you must use the multipath device instead of using the separate multipath legs. Again the /dev/mpathX devnode is just a symlink to some /dev/dm-X device mapper device.

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  • Thus, could I realize that both the /dev/mapper/vg-lv and the /dev/vg/lv are the equivalent FS mounting methods ? – lylklb Feb 26 at 12:47
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    /dev/mapper/vg-lv and /dev/vg/lv are symbolic links, not mounting methods. If the logical volume that they refer to doesn't contain a filesystem, they can't be mounted at all. They are equivalent because they point to the same device file named /dev/dm-# (where # is a number), and they are persistent names. This means you can be certain that they always refer to the same logical volume. /dev/dm-#, on the other hand, is not persistent. – berndbausch Feb 26 at 13:50
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How you mount a filesystem has not much to do with device mapper.

/dev/mapper/vg-lv handles its own multipath I/O? I am not aware of that. Multipath is not handled by LVM, but the DM-multipath module. And that module needs to be configured.

UUID has the demerit of being unwieldy for humans. LABEL addresses that problem. The demerit of LABEL: The humans have to manage the labels and ensure that they are unique.

LVM has the demerit that it doesn't help when your filesystem resides on a non-LVM device. It could be a device that sits on top of a logical volume, for example a LUKS device. LVM's merits are elsewhere. The fact that it offers persistent storage device names is just a nice addition to all the other advantages it has.

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