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

Wed Jul 30 00:33:51 UTC 2014
Benjamin Smith <lists at benjamindsmith.com>

On 07/26/2014 07:04 AM, Jerry Franz wrote:
> 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
That's essentially what we do to re-sync our production file stores. 
Once I move to ZFS, though it won't be an issue.