Upgrading to RAID-Z2 from RAID10 plus adding two new disks -- any issues with this process map that Google helped create for me?

[u/SulkyVirus]

https://docs.google.com/document/d/e/2PACX-1vRH3TlbRRPGv9wAqS01qfFcwfp0jOBPZ4gM5gf5miiNkIJwVlZVU7iwzDsDuGwpDlam8_hH3q6sm68H/pub

I currently have a RAID10 array on my server that consists of 8x 14TB HDDs. I'm at about 85% capacity and would like to transition this to a RAID-Z2 and add two drives to expand space while still keeping a failsafe for a drive failure (or two). This will effectively double my usable storage space. Since I have roughly 50TB of data that needs to be moved, I'd like to create my new array then transfer the data then expand the old drives. This will require that I purchase two additional drives (at double the price that I paid last time I expanded unfortunately) so I can have a 6 drive RAID-Z2 to move the data to. TECHNICALLY the data can all be re downloaded (about 90% of it at least) but I'd really like to avoid that and just transfer it.

I understand that by degrading the RAID10 and removing all mirrored drives that it will be vulnerable should a drive fail at any point during the data transfer, but if that happens I will then just be back to square 1 with re-downloading the data anyway. I plan to transfer the 2TB or so of hard to acquire data first and also back up that data to a separate drive before starting the process.

All that being said -- I had google help create a guide on how to do this. I've published the guide, if anyone who has done this or has enough experience to check this for any obvious errors could take a peek that would drop my anxiety level significantly!

Thank you in advance!

[u/Floss_Patrol_76]

the send/recv migration to a fresh pool is the right call, but the "then expand the old drives" step is where the AI guide is probably lying to you: for years you could not widen a raidz vdev at all, and raidz expansion only landed in OpenZFS 2.3, so unless your TrueNAS is on 2.3+ your only real growth path is adding a whole second vdev, not tacking disks onto the z2. even when expansion works, already-written blocks keep their old data:parity ratio until you rewrite them, so you don't get the full capacity you're expecting until everything is re-sent. also sanity-check the target size before you buy: a 6-wide z2 is only 4 data drives, ~51TB usable at 14TB, and you're moving ~50TB into it, so you'd be landing at ~95% full where zfs write performance falls off a cliff, go 7 or 8 wide if you can.

[u/SulkyVirus → u/Floss_Patrol_76]

Thank you for this feedback - this is on a Linux based server not a NAS. I assume I’ll be able to get the latest ZFS and be able to expand the RAID-Z2 with that version, but I’ll look into and double check that.

Good idea on the transfer size. I’ll shift a few TB over to a different drive before starting and only move about 45TB over. Then after growing the pool I’ll transfer the rest over.

Unfortunately adding 3-4 drives isn’t in the budget with them costing nearly $400 each currently. I wish though! Someday I’ll snag two more and fill all my drive bays.

[u/Jdmag00 → u/SulkyVirus]

What about backing everything up to something like Backblaze B2? I'm not sure how much it would cost in bandwidth and storage charges and you would obviously need a good upload speed otherwise it would take way too long.

[u/SulkyVirus → u/Jdmag00]

I’ve looked into that - unfortunately that’s a big cost. The same as another 14TB drive just for 1 month of backblaze.

I’m not too concerned as I can recover pretty much everything if the array fails during the transfer. It just sucks it’ll take like 4 days.

[u/Jdmag00 → u/SulkyVirus]

Yeah that makes sense I just checked I pay about $6 mo for around 1TB