Still confused about pools, mirrors and replication for backing up data

[celticknot]

Greetings. I may be just dense, or slow, but I do not quite grok the whole zpool, zdev and replication topic. I have read Uncle Festers guide (thanks Uncle!) and noobsause's slide show (Thanks noobsauce!), but I am still not getting it. Here are my specifics and my desires.

Build: FreeNAS-11.1-U6
Platform: Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz (Dell Motherboard)
Memory: 12GB

My original setup was a single 4TB drive. I backed that up a variety of ways, most recently I switched to B2 with cloud sync which is working very well. Now I am running out of space and added a second 4TB drive using volume manager. it loaded as a default of "Striped" and increased my pool to 8TB. So far, so good.

I then bought a new 8TB drive and wanted to mirror the 2x4TB to the 1x8TB so I would have redundancy. According to the noobsauce's slide show, this would be a bad idea, but I did not find that article until AFTER I bought the new drive. I originally thought I could mirror between two zpools so that if ONE drive fails I can recover (1 4TB drive or 1 8TB drive). Perhaps I should have bought 2x4TB drives instead of the single 8TB drive? But in either case, MIRROR is not an option in volume manager when I try adding a drive and now that the 4TB drive is in that pool it is there for good... I can add the new 8TB drive as a seperate pool, but then how do I access it for storage or back ups?

Then I read about using rsync to sync between two pools on a single Freenas box, but I am not certain that is what I want so I am seeking clarification. Is there a way to used the single, 8TB drive as a mirror to the 2x4TB drives (same total storage)? Is there a way to add additional drives in a fashion that will create a mirror or RAID array that provides redundancy? It seems that since I started as a single drive box I am stuck with a single striped pool. I have been reading a bunch of posts and the manual and I am missing something.

I apologize, in advance, for my ignorance but I am just not groking it.

Thank you

Frank

 

[Chris Moore]

Frank,
Sorry, you made a 'rookie mistake'. A single drive, is subject to drive failure or data corruption because you have no redundancy. The thing you need is (at least) a mirrored pair of drives so that you have protection from both data corruption and from a single drive failure destroying all your data.
With two drives in a stripe set, if either drive has a fault, it can damage or destroy all the data. How much data do you have? Is it important to you?

A possible solution would be to get a second 8 TB drive and install the two 8 TB drives as a mirror set, as a new pool. Then move all your data to that pool. Then you can destroy the stripe set and make the two 4 TB drives an additional mirror vdev in your new pool of mirrored vdevs.

If you are having trouble with the terminology, you might want to check this guide:

Terminology and Abbreviations Primer
https://forums.freenas.org/index.php?threads/terminology-and-abbreviations-primer.28174/

There is also this excellent refference that should help you understand:

The ZFS Primer
http://doc.freenas.org/11/zfsprimer.html

This is also a very good introduction:

https://constantin.glez.de/2010/06/04/a-closer-look-zfs-vdevs-and-performance/

 

[celticknot]

Thank you for the information and resources. Now that I have three drives (2x4GB and 1x8 GB) it seems that my best bet may be to back it all up and start from scratch. If I delete my vdev and use those same two drives to make a new, mirrored vdev, can I later add two more drives as a new vdev? Will that vdev be used by freenas? Or am I supposed to just expand the existing vdev using volume manager? I am not clear on how new storage is addressed by Freenas. I am not against starting over, but I would like to be able to use the drives I have and I have four bays available.

Thank you, again, for your time and patience!

--Frank