[CentOS] Convert "bare partition" to RAID1 / mdadm?

[Jerry Franz]

On 07/25/2014 03:33 PM, Benjamin Smith wrote:
> takes between 1 and 2 days, system load depending. We had to give up 
> on rsync for backups in this context a while ago - we just couldn't 
> get a "daily" backup more often then about 2x per week. Now we're 
> using ZFS + send/receive to get daily backup times down into the "sub 
> 60 minutes" range, and I'm just going to bite the bullet and 
> synchronize everything at the application level over the next week. 
> Was just looking for a shortcut...

Here is an evil thought. Is this possible for you do?

1) Setup a method to obtain a RW lock for updates on the original filesystem

2) Use rsync to create a gross copy of the original (yes, it will be 
slightly out of phase,
     but stick with me for a bit) on the new filesystem on top of LVM2 
on top of a RAID1
    volume to make the next step much more efficient.

3) Perform the following loop:
     a) Set the updates lock on original filesystem
     b) rsync a *subset* sub-directory of the original filesystem such 
that you can complete it in, at worst, only a second or two
     c) Rename the original directory to some safe alternative (safety 
first)...
     d) Put a symlink in place of the original directory pointing to the 
newly synced file system sub-directory
     e) Release the mutex lock
     f) Repeat a-e until done

4) Switch over operations to the new filesystem

Another approach would be to leverage something like UnionFS (see 
http://en.wikipedia.org/wiki/UnionFS ) to allow you to both use the 
filesystem *and* automatically propagate all updates to the new volume 
during the migration.

- Jerry Franz