Mirroring: What happens when

[Jerome Salyers]

hi,

i'm running HPUX 11... and i've got mirroring set up, two disc each set...

what happens when i turn off mirroring, make changes to the "main" discs, then everything goes wrong on the main discs... so i want to use my "mirror" discs as a fall back... so, i shutdown the machine, boot onto the "mirror" discs...

now mirroring is still shut off... but all four discs are in...

what happens when i turn on mirroring now? is the data on the "mirror" (still good) disc then sync'd to the "main" (corrupt) discs and all the data on the "main" discs is overwritten with the data from the "mirror" set?

if that's not the case, how can i make it the case?

thanks in advance

jerome

[Pete Randall]

Hi Jerome,

I think you're looking for the capabilities probided by lvmerge, which can be directed to merge either copy to the other - see man lvmerge.


Pete

[Dietmar Konermann · Accepted solution]

Hi, Jerome!

The question is how you "turn off mirroring". Are you assuming an lvsplit or even an lvreduce -m 0?

With hot-pluggable disks I personally prefer this approach... since it needs no configuration change:

- Remove the mirror disks physically, the remaining VG continues running with 2 (original) of 4 disks.

- To estable the mirror (all went fine on the original disks) simply re-insert the mirror disks and perform a vgchange -a y VG + vgsync VG the re-sync starts. Ready.

- To fail back to mirrors (something went wrong on the original disks), halt the system, re-insert the mirror disks, boot from the mirror to LVM maintenance mode, perform a vgcfgrestore on the original disks and then activate the VG using vgchange -a y... now the vgcfgrestore'd (original) disks are considered as completely "stale" and resynced from the mirror disks.

Best regards...
Dietmar.