Feedback/Help with migration plan

[Todd Nine]

Hey guys,
I'm in a situation where I'd like to move from ZFS1 to ZFS2. I had a single drive fail in my ZFS 1, which I've since replaced. It's made me a bit paranoid, so I'd like to move to ZFS2. Below is my disk setup.

Current 4 x 3 TB SSD set up in ZFS 1. Currently using 2.7 TB.

I've purchased another 3 TB SSD, to give me a total of 5. Given that I'm using very little space. My plan is the following.

1. Create a new volume with a single SSD
2. Use ZFS replication to replicate all of my data from my Raid Z2 to the single drive
3. Wipe my Raid Z1 vdev and create a vdev as Raid Z2
4. Use ZFS replication to move my data back
5. Destroy the single drive volume and add to my vdev Raid Z2

I realize I have data loss exposure between steps 2-4. Is there another setup I could do that would mitigate this? I'm assuming not, but wanted to ask someone with more knowledge before I attempt this.

Thanks,
Todd

 

[Dice]

1-4 is fine.
step 5 will not work.

You can not add single drives into raidzX.
If you want a 5 drive in each vdev configured as raidz1 - you'll need to create it with 5 drives.
Same goes for raidz2.

You'll need to offload your data elsewhere in the meantime :)

 

[Todd Nine]

Thanks for the reply @Dice. I have a follow up question. Given that I'm at risk of losing data with > 1 drive failure, Is it possible to create a 5 drive vdev with only 4 drives present? I realize this would put it in an inconsistent state, but pragmatically, I'm no worse off than a ZFS1 state. If I could do this, I could do the following...

3) Create a ZFS2 with 5 drives, 1 that is "failed"
4) Copy my data over
5) Wipe my temporary drive and add it to the ZFS2 Vdev and have 2 drive failure tolerance.

I'm sure it's not possible via the UI, but if it's possible via SSH and the terminal, that would be great.

 

[SweetAndLow]

Just a heads up but zfs1 and zfs2 is not a thing. You probably mean raidz1 vs raidz2. Please try to use the correct terms because it makes a difference.

 

[Dice]

You could toss in another drive of same or higher capacity to create your 5 drive raidz2, do your moving around of data etc and subsequently replace the <tossed in> drive with the intended SSD.

CLI-fu is generally not advisable when doing setups. There are frequently threads on "pragmatic" problems arising from FreeNAS GUI not finding what it expects from under <the hood> as per user <interference>.

 

[Robert Trevellyan]

Create a ZFS2 with 5 drives, 1 that is "failed"

You can't create a failed volume. What you could do is create a RAIDZ2 volume and then shut the system down and physically remove one drive, wipe it, and use it for temporary storage. But I don't see how this gets you closer to your goal.

Just face facts, you need at least one more drive. Choose wisely and you'll be able to implement a backup strategy, which you need anyway, because RAID is not backup.

 

[danb35]

You can't create a failed volume. What you could do is create a RAIDZ2 volume and then shut the system down and physically remove one drive, wipe it, and use it for temporary storage.

...or you could create a sparse file of the appropriate size on the boot pool (zeroes are highly compressible), create the pool with four physical drives and the sparse file, and then offline the file immediately. Not going to get into more detail though because (1) I don't want to take the time to look it up myself, and (2) anybody who had any business trying this should be able to find the threads where it's been discussed anyway.