Question about LVM disk mirroring

[hpuxhelp]

When one break the mirror using (lvreduce -m 0)
and vgreduce to free up the disk, now that disk has free up all its partition. My question, once the pv has physically remove from the vg, can one boot it up using boot alternate mode? I am planning to do update on patches

[Robert-Jan Goossens]

Hi,

Take a look at next discussion.

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x6967c1c4ceddd61190050090279cd0f9,00.html

Robert-Jan.

[Patrick Wallek]

It MIGHT work. The thing I would be concerned about is the lvlnboot and LVM structures on the disk may still contain references to the other disk that may not be valid.

Instead of just reducing the mirror, how about splitting it off via lvsplit? Once your patch update is complete and everything isi working, you can lvmerge them back together.

[Ian Dennison_1]

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0xd17f37f45ef7d4118fef0090279cd0f9,00.html

Try this posting, to check if your mirrored boot disk is valid.

Share and Enjoy! Ian

[Steven E. Protter]

Yes, this is possible, if I understand your question.

Here is a more standard methodology for patching.

make_tape_recovery backup. vg00 only.

Install patches

If the machine won't boot, recover off the Ignite tape.

It's easier than messing around with Mirrors.

We mirror so the system will keep running in the event of a disk or controller failure.

Following your methodoloy, you can lvextend -m 1 after the update once you are happy with what what on.

I've had some issues breaking mirrors, and don't want to be troulbed with it in most cases.

Steve

[hpuxhelp]

Let me rephrase my question in regards to disk mirrorring.
*** I want to update patches and want to using this
method : lvreduce and vgreduce. ( i am currently testign this ). however, thank you for your suggestion on using lvslit



2 disks : one is primary and one is secondary. The primary disk is diskA and secondary disk is diskB. Create a mirror for them. So, let say that I went through the testing process to make sure I can boot on the primary and secondary. Now, currently, the system is boot on primary device. Here is what i want to accomplish at this point :
1. I want to break the mirror for this vg.
2. then vgreduce the primary disk (diskA) out of the volume group. This will leave the vgxx with only diskB.
3. Since now the diskA no longer part of the vg, I have to change the boot using (set boot command ) to set the primary boot to the h/w path of the secondary disk (diskB).
*** I am right on this?
4. So, once if this has been successfully update, I can
bring diskA back and mirror it.
*** How do I know if I am mirroring the new information vs the old information?
** Please check on the step...
pvcreate -B -f /dev/rdsk/cxtxdx...
** If the disk is created without the -f, doesn't it mean it still have information on it. If using pvcreate with -f then, it will initialize the disk and all the information pertains to the disks are no longer available.
** If I am correct on this...
then when to add the disk back and redo the mirroring then -f will be needed. this will do the mirroring of the new information. Is this how to check it ?
-- the rest of the steps on how to create a mirrorI have it under control... :)


5. What if after you have been successfully boot up the system by the secondary disk (diskB), and update the patches and during this process, you screw up very bad causes this disk no longer boot. Now I want to be able to use the mirror on the primary disk to go back where it was from the begining. How would I accomplish this?
would vgcfgrestore work?
I can't use lvextend to extend the bad mirror... so how do I go back to use the good mirror disk that has been remove earlier as I stated...


thank you.