Strange rootvg behaviour

[andy61]

The problem I'm going to outline has been resolved, but I'd be grateful if comeone could shed some light on why the actions worked ! Sorry it's a bit long winded.
We have an AIX 4.3.3 system.We lost a disk (one of two in rootvg), so I in preparation for the replacement I ran unmirrorvg. The command failed saying something along the lines that LVM had encountered an unaccountable error. The errlog showed SCSI BUS errors and a disk operation error for the good disk and filesystem recovery needed entries. No LVM commands worked and no tmp/var files could be created.
Went for reboot ( and the engineer replaced the faulty disk) , but it wouldn't come back (0581 I think), so we went into maintenance mode and fsck'd the filesystems of rootvg. We then got a boot.
Once back, I introduced the newdisk to rootvg and mirrored up ( 3 way as old disk still in rootvg identified by PVID). I went for the mirror first because the last unmirroring operation broke everything. Ran a syncvg against the LVs and all but 2 worked. For those failing ( /usr, /home) it reported it couldn't completely sync the LV. However, once I removed the mirror of the bad disk from those LVs they sync'd up ok.

So, why did removing the mirror definition of a none existent disk - an act I'd assume works only on the ODM and VGDA - resolve the problem and allow me to sync ?

 

[p5wizard]

You made a three-way mirror

[green]good_1st[/green]-[red]bad_2nd[/red]-[blue]new_3rd[/blue]

then you tried to syncvg, which at that point tries to make this into

[green]good_1st[/green]-[green]good_2nd[/green]-[green]good_3rd[/green]

and failed: As the second disk was declared missing, LVM wasn't able to resync the partitions that were identified as "stale" for the 2nd disk. Even with the disk missing, partitions on that disk that haven't yet been touched since it went bad, are still identified as "synced", so your syncvg only complained about a few LVs that had "stale" partitions on the missing disk.

Removing the missing disk from ODM and the VGDA's on the member disks of rootvg cleaned everything up.

Now you have

[green]good_1st[/green]-[green]good_3rd[/green]

but that behaves now as

[green]good_1st[/green]-[green]good_2nd[/green]

All references to the old missing disk have now been cleaned up and you now have a two-way mirror again.


HTH,

p5wizard