Merging two raidz1 vdevs on ZFS to have only ONE redudundant drive

Question

I currently have three 18tb drives under a raidz1 vdev. I bought three new drives to double my space. However when I added these three drives, I can just create a separate raidz1-1. But that means out of the six drives, two will be redundant - not good. I only want one redundant drive!

Here is my current setup:

 state: ONLINE
config:

    NAME                                    STATE     READ WRITE CKSUM
    mass                                    ONLINE       0     0     0
      raidz1-0                              ONLINE       0     0     0
        ata-ST18000NM000J-2TV103_ZR5BBN98   ONLINE       0     0     0
        ata-ST18000NM000J-2TV103_ZR5BLMCR   ONLINE       0     0     0
        ata-WDC_WD181KFGX-68AFPN0_6TGGJ7WC  ONLINE       0     0     0
      raidz1-1                              ONLINE       0     0     0
        sda                                 ONLINE       0     0     0
        sdc                                 ONLINE       0     0     0
        sdd                                 ONLINE       0     0     0
    cache
      nvme1n1                               ONLINE       0     0     0

errors: No known data errors
Filesystem        Size  Used Avail Use% Mounted on
tmpfs             1.6G  2.9M  1.6G   1% /run
/dev/nvme0n1p2    916G   55G  814G   7% /
tmpfs             7.8G     0  7.8G   0% /dev/shm
tmpfs             5.0M  4.0K  5.0M   1% /run/lock
/dev/nvme0n1p1    511M  6.1M  505M   2% /boot/efi
mass               66T   24T   43T  36% /mass
tmpfs             1.6G  112K  1.6G   1% /run/user/1000
//mass/mass        28T   24T  4.6T  84% /media/mass
mass/new_dataset   43T  128K   43T   1% /mass/new_dataset

Does anyone know how I can create one redundancy? Obviously the easiest option would be to move the data, reconfigure, then move it back but I do not have the external space to do that.

I spent an hour on chatgpt but its suggestions would have lost all my data. Eventually saying it's impossible.

So now tapping into the human intelligence out there to see if there is a way to do this or is chatgpt correct in saying it is impossible?

Answer 1

Nope, sorry. You cannot alter vdevs. You also cannot remove vdevs from a pool.

I'm stuck with a similar conundrum: do I go for narrower vdevs at an added cost in terms of disks lost to redundancy, but lowering the cost of future expansions; or broader vdevs, reducing redundancy cost, but increasing the cost of expansion? If I pick smaller vdevs, I'm looking at a cost of four drives in an array of eight, but I'd also more easily be able to expand to twelve disks.

These are the items you must consider before setting up your zpool, because they're tough to hack once it's spinning and full of data.

If it were me, I'd not just take the hit and create the extra raidz1 vdev, but consider setting up a new pool of smaller disks in a raidz2 config. Since I've had two disks fault in the same day in my backup server the other week, I'm convinced that raidz1 makes storage insufficiently robust: I'd have been screwed had I used raidz1.

So take the hit now, and start planning for future upgrades.