Developers Guide

Volume management
11 Dell EMC SC Series with Red Hat Enterprise Linux 7x | CML1071
2.5.2 Universally unique identifier
UUID values exist and persist at multiple layers of volume metadata. UUIDs are created and used by the
device-mapper drivers to uniquely identify and manage each multipath device in Linux. UUIDs are created
within LVM metadata (if the volumes are managed by LVM). UUIDs are also created and managed within the
filesystem layer to uniquely identify each filesystem volume. UUIDs are created dynamically during multipath
definition, LVM, or filesystem creation. Although UUIDs can be changed within each of these layers
independently of other layers, it is not recommended unless its intention is clear and well defined.
Any UUID entries are created in the /dev/disk/by-uuid/ folder. Entries in this folder are created as symbolic
links to their respective devices in the /dev folder.
A sample script in section 2.5.4 parses all Linux multipath device names and presents its multipath UUID, any
known filesystem type, filesystem volume label, and filesystem UUID values to STDOUT.
2.5.3 Persistent naming in /etc/fstab and /boot/grub2/grub.cfg
The LABEL= or UUID= syntax can be used to reference volumes in a variety of places including mount
commands, entries in the /etc/fstab file and /boot/grub2/grub.cfg files or swap partitions. This provides the
liberty of uniquely identifying the volumes regardless of their discovery device name designations, multipath
configurations or predefined multipath aliases.
The following sample /etc/fstab output demonstrates using some of these concepts.
# cat /etc/fstab
[snip]
/dev/mapper/VolGroup00-home /home xfs defaults 1 2
UUID=8284393c-18aa-46ff-9dc4-0357a5ef742d swap swap defaults 0 0
LABEL=TestVol /vol_001 xfs defaults,discard 0 0
[snip]
The following sample /etc/grub2.conf output demonstrates using some of these concepts.
# cat /boot/grub2/grub.cfg
[snip]
linux16 /vmlinuz-3.10.0-123.el7.x86_64 root=UUID=35bea1c0-ce32-42a4-8e36-
72fd5e77471d …
[snip]
Note: It is no longer recommended to manually edit the /boot/grub/grub.cfg file, and instead to use the
grubby command line interface to achieve boot-level configuration changes. The grubby tool manual pages
and help are available with the following commands, respectively: man grubby or grubby --help.