Possible to upgrade a two-drive Mirror to three-drive RAIDZ?

I am starting to play around with a four-bay server with TrueNAS on it. Tomorrow, I am expecting two 12 TB drives from Amazon. Not realizing that TrueNAS does not do JBODs but only the various RAID configurations, I came to the conclusion that I would have to set those up in a Mirror setup.

Once I get a little more pocket money, I am going to buy a third 12 TB drive. Will it be possible to incorporate it into the pool, so that the Mirror is converted into a RAIDZ?

No, this is not possible.

You can do “jbod” aka striping. But only if you like to live dangerous. In other words, dont do it.

Start with the mirror, and then add 2 other drives as mirror to the same pool to increase capacity, or destroy the pool (all data gone) and rebuild as raidz2.

Raidz1 is also not recommend anymore, because of the risk of another drive failing while resilvering. I run a raidz1 but thats only for data i can get back without much hassle.

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So, I really should do RAIDZ2, which means that I would need 4 12-TB disks, if I want an effective 24-TB of storage.

Bah. I have been running RAIDZ1 on 4 2Tb SAS drives for years now and it works perfectly fine. Of course you can always build in more security and i do have a cloud backup of my most important data but what are the chances of 2 drives failing at the same time?

So, could I upgrade a RAIDZ1 to a RAIDZ2 at a later point by adding a fourth drive that I acquire then?

No, you have to stick with what you started with.

Raidz1 is “ok”. Just be aware of the risk in case you need to resilver.

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