topic Re: vgscan at system boot in Operating System - Linux

vgscan at system boot

Ulf Sandberg — Wed, 28 Sep 2005 08:07:43 GMT

I am installing ServiceGuard on RedHat 2.4.21-20. I have problem with "Prevent Boot-Time vgscan". I have followd the instruction on page 40 in Version A.11.16 Release Notes, Second Edition. It dosen't work, some idea?

Re: vgscan at system boot

Steven E. Protter — Wed, 28 Sep 2005 08:31:20 GMT

Are you trying to prevent volume group activation. LVM on HP-UX requires you change auto activation from 1(do it) to 0(don't). The file is /etc/lvmrc

This may be the same on Linux.

SEP

Re: vgscan at system boot

Ulf Sandberg — Wed, 28 Sep 2005 08:37:53 GMT

There is no /etc/lvmrc in RedHat, i have done the chnges in /etc/rc.d/rc.sysinit

Re: vgscan at system boot

Serviceguard for Linux — Thu, 29 Sep 2005 07:19:52 GMT

Please put in a call to support.

I also have asked someone in the lab but it may take a day (or so) to get an answer back here.

Re: vgscan at system boot

Slawomir Gora — Thu, 29 Sep 2005 07:59:23 GMT

Hi,
did you comment both LVM initialization sections in /etc/rc.d/rc.sysinit file ?

Re: vgscan at system boot

Ulf Sandberg — Thu, 29 Sep 2005 08:47:11 GMT

Yes I have now a call at support.
I have done the change on the two places.
I am now running an up2tape, perhaps it will help.

Re: vgscan at system boot

Ulf Sandberg — Wed, 19 Oct 2005 09:01:06 GMT

Here is the solution from HP:
> So the customer has 2 choices:
> - change the "vgchange -ay" command to "vgchange -ay Volume00" in
> initrd-2.4.21-37.ELsmp.img/linuxrc every time a new initrd is created
> - reinstall the system without using LVM for the root filesystem
>
> The script /sbin/mkinitrd, which creates the linuxrc file, could be changed
> to have the required result:
>
> - make a copy of /sbin/mkinitrd
> # mv /sbin/mkinitrd /sbin/mkinitrd.orig
> # cp /sbin/mkinitrd.orig /sbin/mkinitrd
>
> - edit the script /sbin/mkinitrd
> # vi /sbin/mkinitrd
> Change the line:
> echo "vgchange -ay" >> $RCFILE
> To:
> echo "vgchange -ay Volume00" >> $RCFILE
>
> - create a new initrd file with the mkinitrd command or the
> /opt/hp/src/hp_qla2x00src/set_parm command.
>
> - reboot the system

Re: vgscan at system boot

Ulf Sandberg — Wed, 19 Oct 2005 09:05:56 GMT

It is solved by HP support.
I have also made a workaround, that runs
"vgchange -a n my_vg" in rc3.d before the cluster starts.

Re: vgscan at system boot

Matti_Kurkela — Thu, 20 Oct 2005 07:09:44 GMT

Your workaround is not appropriate.

On Linux LVM, the vgchange command will write the new status to disk(s) of the volume group in question.

If your cluster is down, you can get away with your workaround.

But consider a situation when the cluster is active and node A fails. The node B takes over the disks and starts running the application.
You shutdown the node A and do some hardware maintenance. After that, you start it up again.

Now, the disks and the application are active on the node B, so node A *MUST NOT TOUCH* the disks *AT ALL* until node B stops using them.

If you use your workaround, node A will make a mark to the LVM data area of the disk, stating that the volume group is not active... without the knowledge that node B is actually using the disks and the volume group at the time!

With luck, your node B might not notice this immediately... but when it is time to do a LVM operation on node B (say, deactivate the volume group when preparing to move the package back to node A) it will get very confused.

Re: vgscan at system boot

Serviceguard for Linux — Fri, 21 Oct 2005 00:59:07 GMT

Matti,
Did you try this?

One of our engineers did on RedHat 4 (LVM2) and did not see that the deactivate on one node had any affect on the activated volume on the other. We've never seen any problems on RedHat 3. Also, you can deactivate a volume multiple times with no affect.

If you did try this, maybe there is something that we've missed and we may appreceate more details.

Thanks

Re: vgscan at system boot

Ulf Sandberg — Fri, 21 Oct 2005 01:02:12 GMT

Thank you for the information, I see that my workaround is not useable.
I will implement the HP Support solution:

change the "vgchange -ay" command to "vgchange -ay Volume00" in
initrd-2.4.21-37.ELsmp.img/linuxrc every time a new initrd is created

Re: vgscan at system boot

Matti_Kurkela — Mon, 24 Oct 2005 05:02:32 GMT

Sorry, my experience was from older Linux installation. I checked back and found that it was using LVM1.

This seems to have changed in LVM2; if so, that is a good change.

Nevertheless, I would feel uneasy about blindly activating and deactivating cluster VGs while ServiceGuard is not yet running: after all, VG activation is the primary "lock" that prevents the node from writing to the cluster disks.

If this lock is defeated during boot, it may be harmless by itself; but it allows an opportunity for further damage.

For example, at least here I've seen cluster (originally stand-alone application servers, converted to two-node clusters when more availability was needed) in which the cluster volumes were still listed in /etc/fstab. A small mistake, which usually causes some error messages at boot time, nothing more.

If the VG gets activated at boot, this will easily lead to the booting node running a fsck on the cluster disks... while yet unaware that the other node is actively using that disk. This WILL lead to corruption and data loss.