Basic RAID1 doubt

urcindalo · Posted: Tue Oct 07, 2014 9:10 am Post subject: Basic RAID1 doubt

Hi everyone!

I've googled for an answer to my question below but I got lost amidst such technical readings. I use a 2TB internal drive merely for data backup, and I just received today a brand new 2TB external USB drive I'll use as a backup of the internal 2TB drive. I was thinking of raiding both 2TB drives as RAID1, so that I whenever I change something in the internal, the change will be automatically propagated to the external. Both will be formatted as BTRFS.

My question is: what happens if I wanted to work with the internal 2TB drive without plugging in the external USB drive to the computer? Is that possible? Or, will I be able to plug the external drive to another computer and see its content as a regular USB drive?
If that's possible, could I just simply plug the external drive to the computer with the internal RAID1 partner to re-sync the drives?

Again, please excuse me for such a basic question.
Thanks in advance.

vaxbrat · l33t Joined: 05 Oct 2005 Posts: 731 Location: DC Burbs

This is possible but there's no way I would recommend it unless you maybe mount the one drive or the other readonly while the two drives are disconnected. As soon as you mount either one writeable by itself and make changes, you have broken the mirror set. There is no "re-synch" option when this happens, so you are effectively rebuilding the entire mirror each time you do this.

NeddySeagoon · Posted: Tue Oct 07, 2014 7:31 pm Post subject:

urcindalo,

Raid1 is not back up. In fact a single copy is not a backup either.
When the primary fails, you have a copy and no backup.

rm file removes file from all elements of a raid set. The idea of raid is to provide redundency, so the system keeps going if a drive fails.
It lets you choose when to fix it. You still need backups.

Raid over USB is a bad idea as USB is not reliable enough. USB2 does not support DMA either, so its CPU intensive.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

frostschutz · Advocate Joined: 22 Feb 2005 Posts: 2977 Location: Germany

urcindalo · Posted: Wed Oct 08, 2014 11:49 am Post subject:

Thanks for your answers.
The data are personal photos and videos and I just want to have duplicate files in case one of the drives fails. My goal was to achieve it with the less actions on my part.
After reading your explanations I think it will be much easier and convenient for me to use a software solution like luckyBackup to sync both drives whenever I find the need.
Again, thanks very much for your ideas.

RazielFMX · l33t Joined: 23 Apr 2005 Posts: 835 Location: NY, USA

If you have scripting skills, you could write a quick Perl or Shell script that could check to see if the drive is mounted, and if so, do an rsync sans delete option to your external drive of the stuff you care about. You could even put it on cron if you so desired.