Dear community
I soon want to expand my rather simple mirrored x2 4TB storage pool to a RAIDz2 x4 4TB pool.
What is the best approach here in your opinion? All data is backed up, but I have a pretty slow internet connection.
I presume the only way is to copy data from mirrored pool to another drive, make RAIDz2 pool in truenas, and, copy data back to the pool?
Since you have all data backed up, it would be easiest, just to add another mirror vdev to your pool. Giving you the same storage space as a 4 wide raidz2. You can still lose 2 drives, albeit not in the same vdev. Also resilvers of mirrors are alot faster, minimizing the risk of another drive failure during it.
If you only wanna buy 2 new drives and switch to raidz2, there are ways of creating a degraded raidz2 with one old drive and 2 new ones and then adding the 4th later after transferring everything over.
Someone more knowledgeble will surely chime in on that soon…
True on the storage space, but, I would prefer RAIDz2 for the extra redundancy.
Will look into creating the degraded raidz2.
On second thoughts,
Taking into account that my total data is <4TB, I could buy x3 4TB disk. Transfer data to 1 of those disks. Then create a 4 disk RAIDz2 and transfer the data back. It should then also be possible to add the extra disk into the RAIDz2 later making it 5 disk wide? Right?
Only with Truenas Electric Eel. Due to in about 2 weeks.
Nice, time frame is no problem. I think this is best route for me.
Now to gather the hardware 
You don’t need to transfer first. Remove one drive from the mirror and add it to the other three to create a 4-wide raidz2. (Variant: Add to the other three drives and a sparse file to create a degraded 5-wide raidz2; replicate data; then add the last drive to have your 5-wide raidz2 without waiting for Electric Eel.)
The drawback is that you lose redundancy during the process. The more complicated path while keeping redundancy in the process is to create a degraded 4-wide raidz2 with the three new drives while keeping your mirror, replicate, and then add a drive from the former mirror.
Hi
Hi, this sounds rather complicated. I have not created a degraded RAIDz before. Is this possible directly from the GUI? Maybe there is a community guide for SCALE? Although my data is backed up, I would prefer not to take to many risks.
When you say replicate, are you talking rsync? Or what method of replication would you suggest?
That’s because it is. And it is also a “here be dragons!” process not allowed by the GUI.
Roughly (because I guess you’re not going to do it anyway), you create a sparse file of the suitable size to serve as a fake device, create your pool in the CLI including the sparse file, and then offline the file/device.
No one will blame you for avoiding this is and going through a safe road with the GUI. But I thought of this as being “an option”.
ZFS replication of course! You set it as a task in the GUI. It is mostly used as a scheduled task for backups, but you can do it as a manual one-off task as well.
I think the safest and easiest way is to get the drives. Keep one drive from the mirror and use it to replicate the data onto the new RAIDz2 vdev.
Thank you anyways for chipping in with the other options
