[dm-devel] DM-RAID1 data corruption

[malahal at us.ibm.com]

Mikulas Patocka [mpatocka at redhat.com] wrote:
> > > Of course, we can do something in the log itself but it will not fix
> > > "corelog" mirrors, more over the system can't auto recover after a
> > > missing log alone.
> > 
> > Yes, storing information on the log device does not save "corelog"
> > mirrors, so we might need some area to keep information on mirror
> > legs.
> > 
> > Thanks,
> > Taka
> 
> MD-RAID1 solves this problem by having counters in superblocks on both 
> legs. If some leg dies, the counter on the other devices is increased. If 
> the dead disk comes online again, it is found that it has old counter and 
> cannot be trusted.
> 
> Would it be possible to extend a logical volume when converting it to a 
> raid1 and use the last area of the volume as a superblock?
> 
> Mikulas

This is an old thread, I am just trying to revitalize it! :-) How about
dm-raid1 taking superblock storage as arguments in the command line,
just like the log device? The superblock storage is entirely managed by
the kernel, LVM just allocates it. Error handling can be instant this
way. LVM can auto convert the exiting mirrors to this kind of mirrors if
space is available.

Thanks, Malahal.