Need help with adding drives to a ZFS pool

Submitted ⁨⁨7⁩ ⁨months⁩ ago⁩ by ⁨SexualPolytope@lemmy.sdf.org⁩ to ⁨selfhosted@lemmy.world⁩

I have a ZFS pool with two 4TB drives (Seagate IronWold NAS drives) in mirror. I want to double the capacity, so planning of buying two more 4TB drives.

When I bought the those two, I didn’t know much about RAID, and just bought them together. From what I understand now, it’s a bad idea to have disks from same production line in a mirrored vdev since they might fail together.

So, when I get the two new drives, I plan to replace one old drive with a new one, and form another mirror with the rest. That way, there will be one old and one new drive in each vdev. Is this a good plan, or am I just overthinking?

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3dcadmin@lemmy.relayeasy.com ⁨7⁩ ⁨months⁩ ago
If you add 2 more drives surely it would be better to use raidz1? I mean you’d add capacity AND get parity protection so if any 1 drive failed the data would still be safe. 4x4TB drives with raidz1 would give you around 14.5 TB of storage with added security

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- SexualPolytope@lemmy.sdf.org ⁨7⁩ ⁨months⁩ ago
  I don’t think it’ll be ideal. Converting the mirror to z1 would be a big hassle. I don’t see any migration path where I can safely lose a disk without losing data. Also, if both of the old drives fail, I lose everything.
  
  In any case, I’m perfectly happy with 8TB for now. It’s a doubling of my current capacity, of which I’m only using around 70%. I’ll be fine for quite a few years.
  (Also, won’t it be around 12 TB, and not 14.5 TB?)
  
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  - 3dcadmin@lemmy.relayeasy.com ⁨7⁩ ⁨months⁩ ago
    Not if you use raidz1, if you use raidz2 then yes. raidz in zfs is pretty decent. I have had a disk fail in raidz1 and replaced it with another and no data was lost after a resilver. Took a few hours but worked really well. Pretty much the whole idea of using zfs is the enhanced security of your data, seems strange to not put that to good use. The chances of BOTH drives failing before you can replace 1 are very very slim. I get that there is no easy way to just migrate to raidz1 but you could if you got 3 drives, make a new raidz1 pool, copy the data across and then add the old 2 drives to to the pool with a new vdev. You need to be able to add 5 drives to the system though. Of course there are many options here, but you already know that
    
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tofu@lemmy.nocturnal.garden ⁨7⁩ ⁨months⁩ ago
It’s fine to do it that way.

Make sure your pool is healthy, then replace one drive, add the new one to the pool and start resilvering. If something breaks in the resilvering process, you still have the one you took out with all the data.

If you want to be extra sure, copy the whole pool’s content to the fourth drive so even if both old drives fail (unlikely, but as you mentioned, same production line etc, and resilvering is a very read intensive process) you have your data.

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