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?

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.

  • 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
  • 1
    /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

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.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.