Can someone tell me what LVM commands update /etc/lvmtab?

[Jeff.Z]

Hi,

As far as i know, only vgscan/vgimport make changes to lvmtab. How about the regular LVM commands?

vgcreate, vgextend, vgreduce, vgremove, vgsync
lvcreate, lvextend, lvreduce, lvremove...
pvcreate, pvremove, pvmove

can't find any info in Man pages. Any ideas, appreciate.

Thanks,
Jeff

[Pete Randall]

The only command that updates lvmtab is vgscan.


Pete

[Court Campbell]

Well I would think that vgcreate would add entries to lvmtab.

[Jeff.Z]

Court,

Yes, I believe vgcreate should add sth. in lvmtab as lvmtab contains info about VGs/PVs. But, how about vgextend and other commands like vgcfgrestore? Thanks.

Jeff

[Court Campbell]

Any particular reason you want to know this?

[Jeff.Z]

oh yes, when i remove 'ghost disk' using vgreduce -f, the system suggests me to

1. Save /etc/lvmtab to another file.
2. Remove /etc/lvmtab.
3. Use vgscan -v to recreate /etc/lvmtab.
4. NOW use vgcfgbackup(1M) to save the LVM setup.

Should vgreduce update lvmtab automatically?

[Court Campbell]

I think the reasoning has to do with covering your ###. If something were to go awry you could always restore your old lvmtab. vgreduce -f will remove the pv entries of the missing drives from the lvmtab file.

[Jeff.Z]

Court,

yes, vgreduce -f will remove the pv entries of the missing drives from the lvmtab file. That's what i want cuz we have no old lvmtab there and 'Cur PV' > 'Act PV' in vgdisplay. Thanks.

[Court Campbell]

Sorry, but now I am confused. Can you explain your exact issue and what it is you want to achieve.

[Jeff.Z]

Sorry about the confusing...

The 'ghost disk' case has been solved already. We do things like this,

...
# lvreduce -k -m 0 /dev/vg07/odata 0
# vgreduce -f vg07

After 'vgreduce', we got some instructions from the system like this

1. Save /etc/lvmtab to another file.
2. Remove /etc/lvmtab.
3. Use vgscan -v to recreate /etc/lvmtab.
4. NOW use vgcfgbackup(1M) to save the LVM setup.

I did that and everything is ok now. But from what i understand, 'vgreduce' should update /etc/lvmtab automatically same thing as you mentioned what 'vgcreate' did. And i want to know what LVM commands update /etc/lvmtab. Is this clear? Thanks.

[Pete Randall]

Oops - my bad. Obviously I wasn't thinking. Sorry.


Pete

[Court Campbell]

crystal.

[Court Campbell]

Here is a list of what modifies lvmtab.

vgcfgrestore, vgcreate, vgexport, vgextend, vgimport, vgreduce, vgremove, vgscan

I do not believe that any lv/pv commands modify the lvmtab file. Hope that helps.

[Court Campbell]

Actually, scratch vgcfgrestore off that list.

[Jeff.Z]

COOL! Thanks. my last question is, 'vgreduce' modifies lvmtab, why we still need to do the vgscan to re-create /etc/lvmtab following the vgreduce? And we can easily find this kinda suggstions at the very bottom of vgreduce(1M) also. Wired.

[Court Campbell]

You know what. Maybe the -f option only updates the kernel lvm structures. And that would be why you need to recreate the lvmtab file after a forced removal. I don't have a box to test on. Hopefully someone with more knowledge can answer that question.

[Court Campbell · Accepted solution]

Actually, just compare your old lvmtab to your new one and that should answer your question.

[Jeff.Z]

Supper! Thanks a bunch.

[Jeff.Z]

clear now, thanks Court.