OpenZFS on OS X

I have a Drobo5D connected to a Mac Mini (running Catalina). The Drobo recently started rebooting itself every day or so which isn't great for storage reliability(!), and given that Drobo seems to have all but disappeared, I've bought an OWC Thunderbay 8, and was thinking that ZFS would be a good option for my new setup.

I now need to figure out how I should configure ZFS, and how to migrate data from the Drobo to the ZFS setup. I'd appreciate any guidance as I am totally new to ZFS.

Currently on the Drobo I have:
- 2x16TB drives
- 2x10TB drives

For at total of about 32TB storage, of which 16TB is currently used.

I intend to keep these 4 disks (as far as I can tell they are working fine - no SMART warnings), but I need to work out how to move the disks. I do have a backup of the Drobo, but I'm reluctant to wipe the drives as then my backup becomes the only copy of the data, and that seems like it would be tempting fate. From the Drobo's perspective I could
- remove 1 16TB drive
- let the Drobo rebalance, which would give me about 18TB storage (just enough) with 1 disk redundancy
- remove the second 16TB drive (no redundancy on the Drobo, but I still have a separate backup)

I could then use the 2 16TB drives to start my ZFS array, and copy everything over. Once everything is copied over, I could then add the 2 10TB drives to the Thunderbay, but is there any way to add those drives to the same storage pool I've set up with the 16TB drives? I'm aiming for "cost effective redundancy" - i.e. a RAID5 type setup with 4 drives, and 1 providing parity redundancy - but would be OK with no ZFS redundancy while I am transferring. In other words, could I set up a 32TB storage pool (no redundancy) and then add the 2 10TB drives for redundancy?

I'd also appreciate any guidance on how to configure ZFS. I'm aiming for 1 disk redundancy, performance isn't particularly important - the drive is used for archived data and backup. I don't expect to be running short of storage any time soon, but anything I can do now to take advantage of the (soon to be released?) ability for ZFS to expand storage pools would be good to know. Encryption and data compression would be nice, if there are no downsides, but a lot of the archive data is already compressed (zip, gz, compressed disk images, video, photos, audio).

Thanks.

In other words, could I set up a 32TB storage pool (no redundancy) and then add the 2 10TB drives for redundancy?

I don't think this is possible given the limitations you are working within, and the non-expandability of zraid at present. You might like to consider a mirror formation as an alternative. If you took a 16TB and a 10TB drive, and combined them in one pool, copied over your Drobo data, and then used the remaining disks from the Drobo to mirror each of the disks in your new pool, you would have a 4 disk pool consisting of two mirrors, 1 of 16TB and 1 of 10TB, for a total capacity of 26TB (nominally). This leaves you with quite a lot of spare capacity at present, if not quite 16TB. But it also leaves you with the ability to increase the size of the pool as and when you want to, by replacing disks in the mirrors with larger ones.

I used this method to grow an original pool of a 3:3 and 4:4 TB pair of mirrors to its current state of 8:8 and 8:8 TB, all in a Thunderbay 4. I went through additional mirrors which consisted of 4:4, 4:6, 8:6 and finally the 2 8:8s using disks as they became afforadble/available, and repurposing the older disks into a Synology NAS raid which I use to back up the ZFS Pool.

I believe, with the extra capacity you have in a Thunderbay 8, you would be able to add an additional mirror or two as well, giving you an alternative way of expanding the pool.

The other advantage to this configuration is better performance from mirrors than raid, though that is not as much of a consideration in backup or archiving.

Just another option to consider, given zraid growth is not possible at present as far as I know.

Thank you.

Just another option to consider, given zraid growth is not possible at present as far as I know.

It sounds like it will be later this year - but only for raidz not mirrors.

I'd like to leave the option of disk-at-a-time expansion open, so I think I'll order one more 16TB disk now and create a 32TB raidz1 pool. While I am sure that the extra 16TB space will likely take a long time to fill, the 3x3TB drives I started with in my Drobo seemed like more than enough at the time, and assuming that the raidz expansion feature is released by the time I need more space, then I will be able to expand the pool in 16TB chunks which should be a rare event.That said, maybe by then 100TB SSD drives will be so inexpensive that this will all be moot!

Is it possible to create a raidz1 vdev with only 2 drives (albeit in non-redundant mode)? That would allow me to keep the Drobo redundant while copying, and then (after adding the final 16TB disk to the raidz vdev) have the new setup fully redundant before decommissioning the Drobo.

For the benefit of anyone else coming across this, I've completed the Drobo to ZFS disks migration.

I tried creating a test 2-volume raidz1 pool, but funny things happened after adding the 3rd drive (capacities reported were off and in some cases negative), so I didn't go down that route. I was however, able to remove both 16TB drives from the Drobo and together with a new one create a 3x16TB raidz1 array. With some old disks I was able to get the Drobo back to 1 disk redundancy (albeit with very little free space).

Copying everything over with rsync took ages (all told, with time for Drobo resilvering, about 2 weeks), but I've now got everything moved over, and am up and running with ZFS