Configuring an spare disk for vg00

[Fidel Ramirez_1]

Hello,

This HP-UX 11.11 system has two internal drives and vg00 is mirrored on both.
I have an spare disk that I would like to use in case of total disaster and wanted to configure it.
I removed the second disk, plugged in the spare and pvcreate it but when trying restoring the volume group configuration into it doing
vgcfgrestore -n /dev/vg00 /dev/rdsk/c3t6d0
the system complained the drive was already configured.
Does someone has done this before successfully?
I'll appreciate your comments.

Fidel

[S. Ney]

What kind of server do you have? PA-Risc or Itanium? Just for clarification how many available slots in the server, just two? There are different methods available (mirroring, creating an alternate boot disk w/o mirroring) but the how to will be different for PA-Risc and Itanium. Also did you safely reduce the mirror before removing the second disk? Or follow LVM online replacement?

I'd start with two documents not knowing more information about what kind of server you have:
When good disks go bad: Dealing with disk failures under LVM &
LVM Online replacement whitepaper

[Fidel Ramirez_1]

Hi Ney,
This is a RISC system but I have Itanium systems also where I would like to do the same.
There are only two internal slots available already used for vg00.
I didn't reduce the mirror before starting because I thought doing that would leave that disk useless. Is not this right?
I followed an online replacement.

[Steven E. Protter]

Shalom Fidel,

Honestly, mirroring is good enough.

The next step to deal with total disaster is to maintain an Ignite backup of vg00 on tape or another system.

make_tape_recovery # if you have a tape drive
make_net_recovery # to store an image on the network.

More: http://docs.hp.com/en/5992-5230/ch01.html

SEP

[Fidel Ramirez_1]

Hi SEP,

Actually I have configured an Ignite server and every month I run network archives.
Nothing is failing now but my supervisors are being overcautious trying configuring an extra third disk that would be kept in a vault thinking if a total disaster hits then just loading the spare disk into the drive and booting the system will make it available immediately.

[Jim Walls]

Using an Ignite backup is your best solution.

In the event of disaster (fire, flood, earthquake etc) you are unlikely to be able to source an identical replacement server ... technology marches on... so, it may not be possible to boot off your spare disk anyway. An Ignite backup ensures you are able to recover to any compatible hardware.

[Steven E. Protter]

I understand Fidel.

You can dd the boot disk nightly and have a hot spare right in the system.

It is a total waste of time and effort, but you can do that.

You can also use lvextend -m 2 and simply keep two mirror copies of each logical volume and have THREE boot disks.

Disk switching is not a good approach here.

SEP

[Fidel Ramirez_1]

Thank you guys for sharing your time and expertise.
I understand your objections on doing this but ...
SEP, on the lvextend -m 2 approach, is this possible?
There are only two internal slots and the third disk will be plugged just in case.
I have remove a disk to insert the spare. Won't the extents on the removed disk be marked as stale?
After loading the spare, do I have to run pvcreate and vgcfgrestore before lvextend? or just vgcfgrestore because the system will resync with a vgchange -a y?
On a failing test I did on Saturday, I had to mirror again all LVs on vg00 because there were stale extents on the disk I removed.
Is this a reason you are saying disk switching is not recommended here?
The commands I did after inserting the spare were
pvcreate -B
vgcfgrestore
Thank you again,

Fidel

[Emil Velez · Accepted solution]

if this was 11.23 I would suggest Dynamic Root Disk.

Take a downtime window and restore the ignite image to the unused disk (assuming it will fit on that disk).

if you do not touch the other disks you should be able to boot from either the regular boot disk and the mirror or the "extra" boot disk.

if you are careful you can import the disk as a temporary volume group, mount the filesystems temporarily and copy files to the extra boot disk to kind of update its configuration periodically.


This is what some people did before Dynamic root disk.

[Fidel Ramirez_1]

Thank you for your response, Emil.
This system is 11.11 but I got also 11.23 and 11.31.
I got different responses and I'll take time to decide which one is the best option.
Thank you all for your time and collaboration.

Fidel