mdadm raid1, initialize existing drives?

[Fraser Campbell]

On Sunday 12 November 2006 00:41, Jamon Camisso wrote:

> Is it possible to initialize a softraid RAID-1 setup on 2 drives, one of
> which has existing data? Is it a matter of mirroring one drive to the other
> and then running mdadm or would formatting and starting from scratch be a
> better/easier option? Obviously it would be nice to not have to format...

I don't believe that it is possible.  Assuming you have data on sda1 and wish 
to mirror to sdb1, here are the steps I have used in the past:

* step one, make sure you have a full backup of your data on external device
* create a degraded RAID1 (single device using sdb1)
* mirror your data manually (I use tar) from sda1 to your raid device (md0
  perhaps?)
* mount the raid device, reboot, etc ... whatever you wish to be confident
  that your copy is intact (perhaps diff -rq)
* once you're confident that your one-legged raid is good to go bring sda1
  into the fold (used to be raidhotadd, these days it's "mdadm --manage ???")

It would be good (perhaps essential?) to set the partition types on both 
partitions to raid autodetect.

-- 
Fraser Campbell <fraser-Txk5XLRqZ6CsTnJN9+BGXg at public.gmane.org>                 http://www.wehave.net/
Georgetown, Ontario, Canada                               Debian GNU/Linux
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