[linux-lvm] How LVM root volumes gets mounted at boot time ?

[Vivek Satpute]

Hi,

I am seeing that LVM2 is integrated with systemd framework and so
accordingly there are many changes in the way how LVM rootfs volume get
mounted at boot-up time.

For root LVM volume, LVM create virtual block device "/dev/rhel_host/root".
And systemd shows following description of this device.

[root at host vivek]# systemctl show dev-rhel_host-root.device
Id=dev-rhel_host-root.device
Names=dev-rhel_host-root.device
Following=sys-devices-virtual-block-dm\x2d0.device
Description=/dev/rhel_host/root
*LoadState=loaded*
*ActiveState=active*
*SubState=plugged*
InactiveExitTimestamp=Thu 2014-07-24 15:13:50 IST
InactiveExitTimestampMonotonic=17789280
ActiveEnterTimestamp=Thu 2014-07-24 15:13:50 IST
ActiveEnterTimestampMonotonic=17789280
ActiveExitTimestampMonotonic=0
InactiveEnterTimestampMonotonic=0
CanStart=no
CanStop=no
CanReload=no
CanIsolate=no
StopWhenUnneeded=no
RefuseManualStart=no
RefuseManualStop=no
AllowIsolate=no
DefaultDependencies=yes
OnFailureIsolate=no
IgnoreOnIsolate=yes
IgnoreOnSnapshot=yes
NeedDaemonReload=no
JobTimeoutUSec=1min 30s
ConditionTimestampMonotonic=0
ConditionResult=no
Transient=no
*SysFSPath=/sys/devices/virtual/block/dm-0*


I want to know,
1) How systemd and LVM create above dependency of "/dev/rhel_host/root" ?
How "/dev/rhel_host/root" gets SysFsPath "*/sys/devices/virtual/block/dm-0"
? *

2) Which is the udev rule/systemd file creates above dependency (seen by
command "systemctl show dev-rhel_host-root.device").

3) How LVM root volume " /dev/rhel_host/root" gets mounted ? Does it
handled by LVmetaD ?

Any suggestions/inputs would be welcome.


Thanks and Regards,
Vivek
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