how to convert to RAID-1 in place?

[Les Mikesell]

On Sat, 2006-03-25 at 04:53, Roberto Ragusa wrote:
> [...]
> > My understanding is that I can avoid the resizing issue with the RAID-1
> > conversion using the approach of creating the RAID partitions on the second
> > drive and copying the data over to them. Once I can boot from the second
> > drive using the md partitions I can use the partitions on the first drive
> > as spares and not worry about the resizing issue.
> >                  Jack
> 
> Your protocol is good too, the difference is that with your method:
> 
> - disadvantage: you have an extra total file copy, so it takes time
> (copying many small files is much slower than syncing the RAID-1)
> - advantage: you defrag the data
> - disadvantage: you have to be careful with tar flags and you will
> never get a perfectly identical copy (atime, mtime, ctime could be modified)

> Let's say that you're not really converting to RAID-1, you're copying
> everything to your new RAID-1 and then adding your old partitions
> to the RAID-1.

Note that this technique would be the same even if you wanted
to change things like disk sizes or filesystem types so it
is good to understand in any case.   One other quirk about
the tar copy though: if you have an x86_64 system you
probably want to skip /var/log/lastlong if it appears to
be several gigabytes in size and re-create an empty
one on the target drive.  It is a sparse file that doesn't
really take that much space unless you forget the -S option
to tar but even then it will take a long time.

-- 
  Les Mikesell
   lesmikesell at gmail.com