topic Re: Boot from split mirror in Operating System - HP-UX

Boot from split mirror

Mark Nierth — Tue, 21 Oct 2003 16:54:04 GMT

I've got a L class running 11.00. My root volume group is mirrored. As a test, I want to split the mirror, boot from the alternate and then reboot back to the primary and put the mirror back in place. My primary device is c1t2d0 and alternate is c2t2d0. The attachment is what I used to do the split and create a bootable alternate. I'm currently running off the alternate but I see some weird things.
1) lvlnboot -v shows:
Boot Definitions for Volume Group /dev/vg00:
Physical Volumes belonging in Root Volume Group:
/dev/dsk/c1t2d0 (0/0/1/1.2.0) -- Boot Disk
/dev/dsk/c2t2d0 (0/0/2/0.2.0) -- Boot Disk
No Boot Logical Volume configured
Root: lvol3b on: /dev/dsk/c2t2d0
Swap: ??? on: /dev/dsk/c2t2d0
Dump: ??? on: /dev/dsk/c2t2d0
2)vgdisplay -v shows lvol1-8 plus lvol3b-lvol8b. Does not show 1b and 2b.
3) The only file I have in /stand is ioconfig.
4) A dmesg returns Can't get kernal namelist.

Any ideas out there?

Re: Boot from split mirror

Michael Tully — Tue, 21 Oct 2003 17:01:07 GMT

The best way to test the mirror is by:

Take the primary disk out whilst the system is up. It should failover immediately.

The second is to boot off the alternate disk (mirror).

You should never attempt to split a mirror and then boot from it. As you can see, you have some strange results. The 'lvsplit/lvmerge' functions are for splitting the mirror, taking a backup and then merging the pair(s) once again.

Re: Boot from split mirror

Jannik — Tue, 21 Oct 2003 17:15:17 GMT

remember to boot up with hpux -lq
hpux -lq ....

instructs the OS to ignore disk quorum for vg00 when activating the volume group. Normally, more than 50% of the disks which comprise a volume group must be available before a volume group can be activated. Typically in mirrored boot disk configurations, vg00 consists of two disk. If one of these is dead then only 50% of the disks are available; -lq says ignore this and continue. It should be set on both boot disks in a mirrored boot configuration. It is set using the mkboot -a command.

and then mirror to the newly add disk, then you have the primary disk in you hand... That is what you wanted. And you system is again running on primary disk with an alternativ boot mirror.

Re: Boot from split mirror

Mark Nierth — Wed, 22 Oct 2003 13:00:42 GMT

Thanks for the responses. I'm a newbie to the HP-UX world, but I'd read other forum messages that did outline how to split a mirror and then boot from the alternate. Here's what I want to achieve. I need to patch the system and I want a quick way to restore the system in case of problems. I do have ignite backups just in case, but I don't want to wait an hour to get the system restored. The root VG is mirroed and I'm able to boot from the primary and alternate without problems. I do the lvsplit on all the lvols on vg00 followed by fsck's. I patch the system, but decide I need to fall back. I run lvmerge /dev/vg00/lvol? /dev/vg00/lvol?b to get back to the original versions, but I get messages lvmerge: Couldn't reallocate the logical volumes: Device busy. If, for instance, I umount /home, I can run the lvmerge but I'm left with /home mounted on /dev/vg00/lvol4b.
The first question, is using lvsplit/lvmerge to right method of ensuring you have a quick backout in case of problems. 2) How do I overlay the mounted lvols with the backup lvols when I can't umount everything and 3) if all this is possible, how would I rename lvol?b back to lvol?.

Re: Boot from split mirror

Sanjay_6 — Wed, 22 Oct 2003 13:05:58 GMT

Hi,

Here is a doc from hp on this.

http://www1.itrc.hp.com/service/cki/docDisplay.do?docLocale=en_US&docId=200000068695440

The doc id is ULVMKBRC00012525

Hope this helps.

Regds

Re: Boot from split mirror

Vincent DANTEN — Thu, 23 Oct 2003 06:05:18 GMT

Hi,

My opinion about this kind of tests :

Yes should you do it !!

At the beginning, you should verify that you have a real alternate boot disk :

lvlnboot -v : yours seems to be ok

lifls on each boot disk to check the mkboot have been correctly done. You should have at least HPUX.

Then reboot your system, intercept the boot and then make a "sea lif" (search for lif volum), and then boot with "boot P0" or "boot P1" according to the hardware path.

good reboot

Re: Boot from split mirror

Mark Nierth — Thu, 23 Oct 2003 10:04:38 GMT

Thanks for the doc Sanjay...I haven't tried it yet but if I've got to reboot the server 3 times to get back to my original config, I may as well use the Ignite backup. The restore time would probably be pretty close.

Re: Boot from split mirror

pétot stéphane — Thu, 23 Oct 2003 12:55:32 GMT

hi gui,
i m a little bit anxious about the integrity of your system because you said that you have only one file in /stand .
i think there was a problem in your server maybe you have done a "rm" command on your system i hope you have done an gnite tape .

if you don t have any ignite tape or any backup of your system you must find a kernel ( /stand directory ) on an another L class 11.00 and copy it on your sytem. If you don t have a vmunix file in /stand . don t reboot your server it will never start .