topic Re: Missing mirror copy in Operating System - HP-UX

Missing mirror copy

Mike Roger — Tue, 25 May 2004 07:38:24 GMT

I have mirrored all logical volumes for all 6 systems cross 2 EVAs. All primary copy of all LVs are one one EVA and the mirror copies are on the second EVA. Now I have an issue with the second EVA "that has the mirror copies of the LVs" where I have to shut it down. once I do that I will loss the presintation of those LUNs that contain the mirror copies to all six systems. What effect would it make to the UNIX hosts that are running on the primary LVs? OR is it better to split all mirror copies and do the shutdown? From OS side will it panic the systems if you just miss the mirror copy, or it will not effected and it will run only on the primary copy until I bring the other EVA up then do the vgsync?

Re: Missing mirror copy

Marco Santerre — Tue, 25 May 2004 07:45:20 GMT

Though I've never worked with EVA, you shouldn't have to worry about the system panicking, though the system will probably give you tons of messages when you power down your second EVA.

I personnally would go for the safer route which would be to split your mirrors than shut it down, and then resync them afterwards.. but that's just me.

Re: Missing mirror copy

Pete Randall — Tue, 25 May 2004 07:46:06 GMT

It's definitely going to be noticed if the mirrors just go away. I would split them off first.

Pete

Re: Missing mirror copy

Shaikh Imran — Tue, 25 May 2004 07:49:07 GMT

Hi,
I think better to do lvsplit and do the shutdown and Use lvsync to resync them all
There is a possibility of continous error messages in syslog.

Regards

Re: Missing mirror copy

Mike Roger — Tue, 25 May 2004 09:00:18 GMT

Thanks folks, points are assigned

Could you also please refresh my memory of the safest way of doing the lvsplit and lvmerge then lvsync? If you could put it step by step I would appreciated

BR
Mike

Re: Missing mirror copy

Pete Randall — Tue, 25 May 2004 09:11:42 GMT

How about

for LVOL in /dev/vg01/lvol*
do
lvsplit -s backup $LVOL
done

then

for LVOL in /dev/vg01/lvol*
do
lvmerge $LVOLbackup $LVOL
done

Pete

Re: Missing mirror copy

Cesare Salvioni — Tue, 25 May 2004 09:57:21 GMT

My opinion is different from the other.

I think that if u will NOT change the LUN on the second EVA, that is to say when u bring it up the LUN will be exactly as before, tyhere is no need to do anithing: after all mirror (RAID 1) is used exactly to protect in case of missing of one copy !!
The only thing that happens is some messages complaining about a missing copy but the system go on using the working copy of the lv.
When the copy is available again, LVM will sync the LVs and everything is back. In the worst case LV will not sync the copies automatically and u have to run the command vgsync.

If u r planning to change the LUN of the second EVA, splitting and merging is non sense. If u change the LUNs, the PV will be not valid: u have to lvreduce -m 1 all the LVs (reducing the mirror copy) and vgreduce also to deallocate the PV from the VG.

What i'm trying to say is that if u can lvmerge after the power up there is no need to lvsplit before. If the EVA change the configuration u will not see the PV in the VG so u will not be able to lvmerge after

hope this help
Cesare Salvioni

Re: Missing mirror copy

Thork — Wed, 26 May 2004 09:27:26 GMT

Dear Mike Roger,

Like Cesare Salvioni, Iâ m sure that you donâ t have to worried by this.
When you have two or more disk in mirror and lose one copy, when the copy is available again, LVM will sync the LVs.
But be careful that only in two cases the LVs will synchronize automatically:
- When a disk comes back online after experiencing a power failure.
- When you extend a logical volume by increasing the number of mirror copies â the newly added physical extents will be synchronized.

If you have to synchronize your LVs manually you must use the vgsync command or the lvsync command.

Itâ s necessary that you check the Recovery Method used in the LVs definitio