what role does each lvm daemon.

[Jason Kang]

Hi..
I'm searching for process lists in one of my servers.
I'm wondering What role do lvm daemons.
I executed 'ps -ef | grep lvm '

root 19 0 0 Nov 18 ? 0:50 lvmkd
root 20 0 0 Nov 18 ? 0:50 lvmkd
root 21 0 0 Nov 18 ? 0:51 lvmkd
root 22 0 0 Nov 18 ? 0:50 lvmkd
root 23 0 0 Nov 18 ? 0:50 lvmkd
root 24 0 0 Nov 18 ? 0:50 lvmkd
root 25 0 0 Nov 18 ? 1:23 lvmschedd
root 27 0 0 Nov 18 ? 0:11 lvmdevd
root 28 0 0 Nov 18 ? 0:00 lvmattachd
root 71 0 0 Nov 18 ? 1:44 lvmdevd
root 72 0 0 Nov 18 ? 0:00 lvmattachd

I just guess that lvmattachd and lvmdevd are created per 1 volume group.
also, lvmattachd is related alternate link.

I want to know what role is exactly each lvm daemons( lvmkd, lvmschedd, lvmdevd, lvmattschd,cmlvmd etc..)

[R.K. # · Accepted solution]

Hi Jason,

lvmkd : The lvmkd's are daemon processes that watch a queue. When a job
arrives in the queue an lvmkd launches the job as a process,
which is now managed by the kernel and is subject to the normal
priority and CPU constraints as other processes.
More details:
http://forums13.itrc.hp.com/service/forums/questionanswer.do?threadId=96204

lvmdevd : is a LVM device update/recovery daemon. One per each group.

lvmattachd : this daemons is for watching physical volumes, marked as NOT_ATTACHED and attach it back to the volume group. For example when link disappear from SAN LUN's.

lvmschedd : A special "lvmschedd" daemon was created to make periodic calls to reschedule LVM I/Os. This eliminates the potential deadlock.
PHKL_35970 : 11.11 : lvm cumulative

[Michael Steele_2]

Hi




LVM
LVM is a kernel driver (not to be confused with the LVMKD that's used for overhead and other special cases).

http://www11.itrc.hp.com/service/cki/docDisplay.do?docLocale=en&docId=emr_na-c01011375

lvmkd
The lvmkd's are daemon processes that watch a queue. When a job arrives in the queue an lvmkd launches the job as a process, which is now managed by the kernel and is subject to the normal priority and CPU constraints as other processes

http://www11.itrc.hp.com/service/cki/docDisplay.do?docLocale=en&docId=emr_na-c00999979

In short, any lvm specific command goes through lvmkd, i.e., activating a vg.

lvmattachd
Introduced a new kernel daemon which will keep track of NOT_ATTACHED PVs (* Alternate PV links *)and attach them to the VG as soon as they become accessible. This will avoid the need to reactivate.

lvmschedd
Scheduling daemon for LVM

I could find no references for lvmdevd or lvmschedd. However, its obvious they all work together to make the LVM driver work: They are threads internal to the LVM driver.

If you are concerned then update you LVM patches. There are many.

Looking around, your list of lvm processes appear light. If you get a ton, then maybe you've got disk or disk I/O issues.

[R.K. #]

Hi Again,

Just had some research.

>>lvmattachd and lvmdevd are created per 1 volume group.


SERVER 11.11 L3000
# vgdisplay -v | grep -i "vg name" ; ps -ef | grep -i -e lvmattachd -e lvmdevd
VG Name /dev/vg00
VG Name /dev/vg01
root 28 0 0 Nov 2 ? 0:00 lvmdevd
root 29 0 0 Nov 2 ? 0:00 lvmattachd
root 65 0 0 Nov 2 ? 0:00 lvmdevd
root 66 0 0 Nov 2 ? 0:00 lvmattachd


SERVER 11.11 L3000 (After Deactivating VG01)
# vgchange -a n vg01
Volume group "vg01" has been successfully changed.
# vgdisplay -v | grep -i "vg name" ; ps -ef | grep -i -e lvmattachd -e lvmdevd
vgdisplay: Volume group not activated.
vgdisplay: Cannot display volume group "/dev/vg01".
VG Name /dev/vg00
root 28 0 0 Nov 2 ? 0:00 lvmdevd
root 29 0 0 Nov 2 ? 0:00 lvmattachd

So we can say that lvmattchd and lvmdevd are created one per Volume Group

[Jason Kang]

Thank you for your advices.

i learned to many thing about lvm daemons.

I have an additional question.

There are 6 lvmkd processes in memory.

Why are 6 processes runnging?

Is it a default value?

and If one of lvmkd processes is down. What happen?( os failure or downed process restarts etc..)

Have a Nice day~!

[NouZ]

i think "lvmkd"'s 6 instants will be there in all server , even i can see the same .

>ps -ef | grep lvmkd
root 19 0 0 18:24:25 ? 0:00 lvmkd
root 20 0 0 18:24:25 ? 0:00 lvmkd
root 21 0 0 18:24:25 ? 0:00 lvmkd
root 22 0 0 18:24:25 ? 0:00 lvmkd
root 23 0 0 18:24:25 ? 0:00 lvmkd
root 24 0 0 18:24:25 ? 0:00 lvmkd
root 4972 3478 1 20:42:48 pts/ta 0:00 grep lvmkd