In Goldeye 25.10.2, I have a 3x mirror consisting of 3 Seagate Ironwolf Pro 12TB HDDs for 12TB total capacity. It’s up to almost 70 percent full, so I’m considering buying a fourth 12TB Ironwolf and moving to a 4-drive Z2 single VDEV pool, for 24TB total capacity.
The way I’m considering migrating involves using a USB drive in some interim steps. I would like to see if people think this migration approach makes sense.
Here is how I plan to migrate: (1) install the new 12TB drive. (2) detach two drives from the existing 3x mirror so that the existing pool will become just a single 12TB drive holding all datasets. (3) connect an 18TB USB drive that I have sitting around. (4) Create a 4-drive Z2 pool consisting of the three free 12TB SATA HDDs and the 18TB USB drive. (5) Replicate all datasets from the old pool, which will be down to one drive, to the new 4-drive Z2 pool, (6) In the Truenas UI, transfer all data protection tasks (snapshot, cloud backup, rsync, replicate) from the old pool to the new pool, (7) destroy the old pool, thus freeing up the remaining 12TB drive. (8) detach the 18TB USB drive from the 4-drive Z2 pool, thus sending it into a degraded state. (9) replace the 18TB USB drive with the remaining 12Tb HDD. (10) Disconnect the USB drive.
Does the above migration make sense?
Also, please note that I’m not worried about data loss despite going down to a one drive pool at one point because I have numerous backups of this data, both on-site and in the cloud.
Yes, in theory, that will work. I would make sure a scrub has been done recently, within the last 2 weeks. If not, run one before detaching the Mirror devices.
There are slight improvements. If you replicate the pool exactly, then you don’t need to change the GUI’s options for shares and such. You can export your degraded Mirror pool, and remove that disk. Then using the command line import the new pool with the old pool’s name, and export again. Then in the GUI import the newly renamed pool back as if it was the old pool. Complicated, but doable.
A different way is to use a 4 disk RAID-Z2 with a degraded vDev. Meaning you have 3 real disks, with 1 being a fake disk. This is more for advanced users, as it does require making a TrueNAS compatible pool from the command line. As well as a fake disk that you remove after pool creation.
Doing this removes the needs for the USB attached drive, which may slow down the pool’s copy. (Or may not…)
Honestly, I’ve seen so many posts asking about this exact scenario, then I feel like it should just be added to the GUI with a disclaimer that IxSystems does not endorse nor recommend doing it this way.
Patrick Hausen: are you suggesting that I offline the USB drive before doing the replication? I had planned to leave the USB drive online as part of the 4-drive Z2 pool until the replication is completed, and then detach or offline it and replace it with the newly free SATA drive.
Yes. The USB drive as a live part of your RAIDZ2 pool will affect replication performance in a very bad way. And if you just pull it you still have redundancy. Only the pool can be written to much faster.
