[CentOS] Moving from mdadm raid 0 to single disk

Wed Jan 12 01:20:34 UTC 2022
Jonathan Billings <billings at negate.org>

On Jan 11, 2022, at 20:11, Alexandre Leonenko <alex at esecuredata.com> wrote:
> Hopefully a quick question. I'm going to move the filesystem of a raid 0 mdadm to a single disk.
> The filesystem is just a data drive, can I just dd if=/dev/md0 of=/dev/sdc ?
> Or should I rather rsync the files directly?

You should use whatever appropriate tools to copy the files directly.

 The “dd” program is not a backup or data transfer program. It is especially bad for your request. If you did that, you’d be copying every bit on the disk, whether it is used or not.  It would get hung up and exit prematurely if it encountered a bad sector (even if the filesystem had it marked in the list of bad blocks). It would create a disk layout that could potentially have significantly worse performance. 

Better to create a proper partition table and filesystem(s), optimized to the new disk, and use one of the many tools to copy over the actual data. Use the file system’s dump/restore, tar, rsync, etc. 

There are a small number of cases where “dd” is the right tool. Backups and data transfer is not one of them. 

Jonathan Billings